Online Etymology Dictionary

knocker (n.): late 14c., agent noun from knock (v.). Sense of "door banger" is by 1590s. Knockers "a woman's breasts" is slang attested from 1941.
entrance (n.): 1520s, "act of entering," from Middle French entrance, from entrer (see enter). Sense of "door, gate" first recorded in English 1530s. Meaning "a coming of an actor upon the stage" is from c. 1600.
matchlock (n.): 1690s, from match (n.1), in reference to the firing mechanism, + lock (n.1) in the firearm sense (1540s); probably so called for its resemblance to a door-latching device.
haggaday (n.): mid-14c., "a kind of door latch," and said to be still the name for rings for raising thumb-latches in the north of England. It appears to be what it looks like: what you say when you open the door ("have good day," as in the 1414 record of them as hafgooddays).
usher (n.): late 13c., "servant who has charge of doors and admits people to a chamber, hall, etc.," from Anglo-French usser (12c.), Old French ussier, uissier "porter, doorman," from Vulgar Latin *ustiarius "doorkeeper," variant of Latin ostiarius "door-keeper," from ostium "door, entrance," from os "mouth," from PIE *os- "mouth" (see oral). Fem. form usherette is attested from 1913, American English.
valve (n.): late 14c., "one of the halves of a folding door," from Latin valva (plural valvae) "section of a folding or revolving door," literally "that which turns," related to volvere "to roll" (see volvox). Sense extended 1610s to "membranous fold regulating flow of bodily fluids;" 1650s to "mechanical device that works like an anatomical valve;" and 1660s in zoology to "halves of a hinged shell." Related: Valved.
hinge (n.): c. 1300, "the axis of the earth;" late 14c. as "movable joint of a gate or door," not found in Old English, cognate with Middle Dutch henghe "hook, handle," Middle Low German henge "hinge," from Proto-Germanic *hanhan (transitive), *hangen (intransitive), from PIE *konk- "to hang" (see hang (v.)). The notion is the thing from which a door hangs. Figurative sense of "that on which events, etc., turn" is from c.1600. Stamp-collecting sense is from 1883.
port (n.2): "gateway," Old English port "portal, door, gate, entrance," from Old French porte "gate, entrance," from Latin porta "city gate, gate; door, entrance," from PIE root *per- (2) "to lead, pass over" (see port (n.1)). Specific meaning "porthole, opening in the side of a ship" is attested from c. 1300.
canteen (n.): c. 1710, "store in a military camp," from French cantine "sutler's shop" (17c.), from Italian cantina "wine cellar, vault," which is perhaps another of the many meanings that were attached to Latin canto "corner;" in this case, perhaps "corner for storage." A Gaulish origin also has been proposed. Extended to "refreshment room at a military base, school, etc." from 1870. Meaning "small tin for water or liquor, carried by soldiers on the march, campers, etc." is from 1744, from a sense in French.
filet (n.): 1841 in cookery, reborrowing from French of the same word that had been taken 14c. and Englished as fillet (q.v.). Filet mignon is attested as a French word in English from 1815.
The 'Chateaubriand,' the 'entrecôte,' and the 'filet mignon' (of mutton), with other forms, are all due to the more enlarged sympathies of the French butcher for what is perfect. We must entirely change the mode of cutting up the carcase before we can arrive at the same perfection in form of meat purchasable, and as that is hopeless, so is it useless to insist further on the subject on behalf of the public. ["The Kitchen and the Cellar," "Quarterly Review," April 1877]
unhinge (v.): recorded earlier in the mental sense of "to disorder" the mind, etc. (1612) than in the literal one of "to take (a door, etc.) off its hinges" (1616); from un- (2) "opposite of" + hinge (n.). Hinge as a verb meaning "to attach by a hinge" is recorded only from 1758. Related: Unhinged; unhinging.
delta (n.): c. 1200, Greek letter shaped like a triangle, equivalent to our "D," the name from Phoenician daleth "tent door." Herodotus used it of the mouth of the Nile, and it was so used in English from 1550s; applied to other river mouths from 1790.
opportunity (n.): late 14c., from Old French opportunite (13c.) and directly from Latin opportunitatem (nominative opportunitas) "fitness, convenience, suitableness, favorable time," from opportunus (see opportune). Opportunity cost attested from 1911. Expression opportunity knocks but once (at any man's door) attested from 1898.
ajar (adv.): "slightly open," 1718, also on a jar, on the jar, perhaps from Scottish dialectal a char "turned a little way," earlier on char (early 16c.), "on the turn (of a door or gate)," from Middle English char, from Old English cier "a turn."
mooreeffoc (n.): "coffee-room, viewed from the inside through a glass door, as it was seen by Dickens on a dark London day; ... used by Chesterton to denote the queerness of things that have become trite, when they are seen suddenly from a new angle." [J.R.R. Tolkien]
porter (n.2): "doorkeeper, janitor," mid-13c. (late 12c. as a surname), from Anglo-French portour, Old French portier "gatekeeper" (12c.), from Late Latin portarius "gatekeeper," from Latin porta "city gate, gate; door, entrance," from PIE root *per- (2) "to lead, pass over" (see port (n.1)).
transom (n.): late 14c., transeyn "crossbeam spanning an opening, lintel," probably by dissimilation from Latin transtrum "crossbeam" (especially one spanning an opening), from trans- "across" (see trans-) + instrumental suffix -trum. Meaning "small window over a door or other window" is first recorded 1844.
undo (v.): Old English undon "to unfasten and open" (a window or door), "to unfasten by releasing from a fixed position; to cancel, discharge, abrogate, reverse what has been done, put back in a former condition; bring to ruin, destroy," from un- (2) "opposite of" + do (v.). Related: Undone; undoing.
sash (n.2): framed part of a window, 1680s, sashes, mangled Englishing of French châssis "frame" of a window or door (see chassis). French word taken as a plural and -s trimmed off by 1704. Sash-weight attested from 1737.
D: fourth letter of the Roman alphabet, from Greek delta, from Phoenician and Hebrew daleth, pausal form of deleth "door," so called from its shape. The sign for "500" in Roman numerals. 3-D for "three-dimensional" is attested from 1952.
coupe (n.): 1834, from French coupe (18c.), noun use of past participle of couper "to cut (in half);" see coup. Modern use is from early 19c. carrosse coupe "cut-off carriage," a shorter version of the berlin, minus the back seat. First applied to closed two-door automobiles 1897.
ledge (n.): late 13c., "crossbar on a door," perhaps [OED] from the Middle English verb leggen "to place, lay" (see lay (v.), and compare ledger). Others suggest a Scandinavian source cognate with Swedish lagg "the rim of a cask." Sense of "narrow shelf" is first recorded 1550s; that of "shelf-like projection of rock" is from 1550s.
wicket (n.): early 13c., "small door or gate," especially one forming part of a larger one, from Anglo-French wiket, Old North French wiket (Old French guichet, Norman viquet) "small door, wicket, wicket gate," probably from Proto-Germanic *wik- (source also of Old Norse vik "nook," Old English wican "to give way, yield"), from PIE root *weik- (4) "to bend, wind" (see weak). The notion is of "something that turns." Cricket sense of "set of three sticks defended by the batsman" is recorded from 1733; hence many figurative phrases in British English.
hurdle (n.): Old English hyrdel "frame of intertwined twigs used as a temporary barrier," diminutive of hyrd "door," from Proto-Germanic *hurdiz "wickerwork frame, hurdle" (source also of Old Saxon hurth "plaiting, netting," Dutch horde "wickerwork," German Hürde "hurdle, fold, pen;" Old Norse hurð, Gothic haurds "door"), from PIE *krtis (source also of Latin cratis "hurdle, wickerwork," Greek kartalos "a kind of basket," kyrtos "fishing creel"), from root *kert- "to weave, twist together" (source also of Sanskrit krt "to spin").

Used as temporary fencing in agriculture. Sense of "barrier to jump in a race" is by 1822 (hurdle-race also is from 1822); hurdles as a type of race (originally horse race) with hurdles as obstacles is attested by 1836. Figurative sense of "obstacle" is 1924.
hake (n.): type of sea fish, late 13c., probably from Old English haca "a hook, door-fastening" (related to hacod "pike" the fish), or from cognate Old Norse haki "hook;" in either case the fish so called from the shape of its jaw; both from Proto-Germanic *hakan (cognate with Dutch hake "hook"), from PIE root *keg- "hook, tooth" (see hook (n.)).
knock (v.): Old English cnocian (West Saxon cnucian), "to pound, beat; knock (on a door)," likely of imitative origin. Figurative meaning "deprecate, put down" is from 1892. Related: Knocked; knocking. Of engines from 1869. To knock back (a drink) "swallow quickly or at a gulp" is from 1931. Many phrases are in reference to the auctioneer's hammer, for example knock down (v.) "dispose of (something) at auction" (1760).
janitor (n.): 1580s, "an usher in a school," later "doorkeeper" (1620s), from Latin ianitor "doorkeeper, porter," from ianua "door, entrance, gate," from ianus "arched passageway, arcade" (see Janus) + agent suffix -tor. Meaning "caretaker of a building, man employed to see that rooms are kept clean and in order" first recorded 1708. Fem. forms were janitress (1806), janitrix (1818).
panel (n.): early 14c., from Old French panel "piece of cloth, piece, saddle cushion" (Modern French panneau), from Vulgar Latin *pannellus, diminutive of Latin pannus "piece of cloth" (see pane). Anglo-French legalese sense of "piece of parchment (cloth) listing jurors" led by late 14c. to meaning "jury." General sense of "persons called on to advise, judge, discuss," etc. is from 1570s. Sense of "distinct part of surface of a wall, door, etc." is first recorded c. 1600.
hatch (n.1): "opening, grated gate, half-door," Old English hæc (genitive hæcce) "fence, grating, gate," from Proto-Germanic *hak- (source also of Middle High German heck, Dutch hek "fence, gate"), a word of uncertain origin. This apparently is the source of many of the Hatcher surnames; "one who lives near a gate." Sense of "opening in a ship's deck" is first recorded mid-13c. Drinking phrase down the hatch attested by 1931 (the image is nautical).
opening (n.): Old English openung "act of opening" (a door, mouth, etc.), "disclosure, manifestation," verbal noun from present participle of open (v.). Meaning "vacant space, hole, aperture, doorway" is attested from c. 1200. Meaning "act of opening (a place, to the public)" is from late 14c. Sense of "action of beginning (something)" is from 1712; meaning "first performance of a play" is 1855; "start of an art exhibit" is from 1905. Sense of "opportunity, chance" is from 1793.
grate (n.): late 14c., "grill for cooking;" early 15c., "iron bars or cagework across a door or window," from Anglo-Latin (mid-14c.), from Old French grate or directly from Medieval Latin grata "a grating, lattice," from Latin cratis "wickerwork, hurdle" (see hurdle (n.)). As a verb meaning "to fit with a grate," from mid-15c. Related: Grated; grating.
locket (n.): mid-14c., "iron cross-bar of a window," from Old French loquet "door-handle, bolt, latch," diminutive of loc "lock, latch," from Frankish or some other Germanic source (compare Old Norse lok "fastening, lock;" see lock (n.1)). Meaning "ornamental case with hinged cover" (containing a lock of hair, miniature portrait, etc.) first recorded 1670s.
clique (n.): 1711, "a party of persons; a small set, especially one associating for exclusivity," from obsolete French clique, originally (14c.) "a sharp noise," also "latch, bolt of a door," from Old French cliquer "click, clatter, crackle, clink," 13c., echoic. Apparently this word was at one time treated in French as the equivalent of claque (q.v.) and partook of that word's theatrical sense.
porch (n.): c. 1300, "covered entrance," from Old French porche "porch, vestibule," from Latin porticus "covered gallery, covered walk between columns, arcade, portico, porch," from porta "city gate, gate; door, entrance," from PIE root *per- (2) "to lead, pass over" (see port (n.1)). The Latin word was borrowed directly into Old English as portic.
Star Chamber (n.): late 14c., apartment in the royal palace at Westminster in which members of the king's council sat to exercise jurisdiction 14-15c., it evolved 15c. into a court of criminal jurisdiction, infamous under James I and Charles I for arbitrary and oppressive proceedings. Abolished 1641. Supposedly so called because gilt stars had been painted on the ceiling. Later there was a star on the door.
slam (n.1): 1670s, "a severe blow," probably from a Scandinavian source (compare Norwegian slamre, Swedish slemma "to slam, bang") of imitative origin. Meaning "a violent closing of a door" is from 1817. Meaning "an insult, put-down" is from 1884. Slam-bang recorded by 1806 (also slap-bang, 1785). Slam-dunk is from 1976; early use often in reference to Julius Erving. Slam-dance is attested by 1987 (slam by itself in this sense is recorded from 1983).
rapper (n.): agent noun meaning "one who raps" in any sense (see rap (v.)). Before the hip-hop performance sense emerged c. 1979, it could mean "door-knocker" (1630s), "spirit-rapper" (1755), "professional perjurer" (1840), prison slang for "prosecutor" (1904), "itinerant antiques buyer," with a tinge of shadiness (1914). Rapster is from 1772.
catch (n.): late 14c., "device to hold a latch of a door," also "a trap;" also "a fishing vessel," from catch (v.). Meaning "action of catching" attested from 1570s. Meaning "that which is caught or worth catching" (later especially of spouses) is from 1590s. Sense of "hidden cost, qualification, etc." is slang first recorded 1855 in P.T. Barnum.
lintel (n.): "horizontal piece resting on the jambs of a door or window," early 14c., from Old French lintel "threshold" (13c., Modern French linteau), a word of uncertain origin, probably a variant of lintier, from Vulgar Latin *limitalis "threshold," or a similar unrecorded word, from Latin limitaris (adj.) "that is on the border," from limes (genitive limitis) "border, boundary" (see limit (n.)). Altered by influence of Latin limen "threshold."
obstacle (n.): mid-14c., from Old French obstacle, ostacle "opposition, obstruction, hindrance" (13c.) or directly from Latin obstaculum "a hindrance, obstacle," with instrumental suffix *-tlom + obstare "stand before, stand opposite to, block, hinder, thwart," from ob "against" (see ob-) + stare "to stand," from PIE root *stā- "to stand" (see stet).
The lover thinks more often of reaching his mistress than the husband of guarding his wife; the prisoner thinks more often of escaping than the gaoler of shutting his door; and so, whatever the obstacles may be, the lover and the prisoner ought to succeed. [Stendhal, "Charterhouse of Parma"]
Obstacle course is attested from 1891.
harmony (n.): late 14c., "combination of tones pleasing to the ear," from Old French harmonie, armonie "harmony," also the name of a musical instrument (12c.), from Latin harmonia, from Greek harmonia "agreement, concord of sounds," also as a proper name, the personification of music, literally "means of joining," used of ship-planks, etc., also "settled government, order," related to harmos "fastenings of a door; shoulder," from PIE *ar-ti-, from *ar- "to fit together" (see arm (n.1)). Modern scientific harmony, using combinations of notes to form chords, is from 16c. Sense of "agreement of feeling, concord" is from late 14c.
mallet (n.): late 14c., from Old French maillet "mallet, small wooden hammer, door-knocker," diminutive of mail, from Latin malleus "a hammer," from PIE *mal-ni-, from root *mel- (1) "soft," with derivatives referring to softened material and tools for grinding (source also of Hittite mallanzi "they grind;" Armenian malem "I crush, bruise;" Greek malakos "soft," mylos "millstone;" Latin molere "to grind," mola "millstone, mill," milium "millet;" Old English melu "meal, flour;" Albanian miel "meal, flour;" Old Church Slavonic meljo, Lithuanian malu "to grind;" Old Church Slavonic mlatu, Russian molotu "hammer").
mouth (n.): Old English muþ "mouth, opening, door, gate," from Proto-Germanic *munthaz (source also of Old Saxon, Old Frisian muth, Old Norse munnr, Danish mund, Middle Dutch mont, Dutch mond, Old High German mund, German Mund, Gothic munþs "mouth"), with characteristic loss of nasal consonant in Old English (compare tooth, goose), from PIE *mnto-s (source also of Latin mentum "chin"). In the sense of "outfall of a river" it is attested from late Old English; as the opening of anything with capacity (a bottle, cave, etc.) it is recorded from c. 1200. Mouth-organ attested from 1660s.
post (n.1): "a timber set upright," from Old English post "pillar, doorpost," and Old French post "post, upright beam," both from Latin postis "door, post, doorpost," perhaps from por- "forth" (see pro-) + stare "to stand," from PIE root *stā- "to stand, set down, make or be firm" (see stet).

Similar compounds are Sanskrit prstham "back, roof, peak," Avestan parshti "back," Greek pastas "porch in front of a house, colonnade," Middle High German virst "ridepole," Lithuanian pirstas, Old Church Slavonic pristu "finger" (PIE *por-st-i-).
tail-gate (n.): 1868, back panel on a wagon, hinged to swing down and open, from tail (n.1) + gate (n.). Extended by 1950 to hatchback door on an automobile. The verb (also tailgate) meaning "to drive too close behind another vehicle" is from 1951 ("Truck drivers know the practice of following too close as tail-gating" - "Popular Science," Jan. 1952); as an adjective, in reference to the open tail-gate of a parked car as a setting for a party or picnic, from 1958. Related: Tail-gating.
sesame (n.): early 15c., probably from Middle French sisame and directly from Latin sesamum (nominative sesama), from Greek sesamon (Doric sasamon) "seed or fruit of the sesame plant," a very early borrowing via Phoenician from Late Babylonian *shawash-shammu (compare Assyrian shamash-shammu "sesame," literally "oil-seed"). First as a magic password in 1785 translation of Galland's "Mille et une nuits," where it opens the door of the thieves' den in "Ali Baba and the Forty Thieves." Phrase open sesame current since about 1826.
shut (v.): Old English scyttan "to put (a bolt) in place so as to fasten a door or gate, bolt, shut to; discharge, pay off," from West Germanic *skutjan (source also of Old Frisian schetta, Middle Dutch schutten "to shut, shut up, obstruct"), from PIE *skeud- "to shoot, chase, throw" (see shoot (v.)). Related: Shutting.

Meaning "to close by folding or bringing together" is from mid-14c. Meaning "prevent ingress and egress" is from mid-14c. Sense of "to set (someone) free (from)" (c. 1500) is obsolete except in dialectal phrases such as to get shut of. To shut (one's) mouth "desist from speaking" is recorded from mid-14c.
latch-key (n.): also latchkey, "a key to raise or draw back the latch of a door" and allow one to enter from outside, 1825, from latch (n.) + key (n.1). Latchkey child first recorded 1944, American English, in reference to children coming home from school while both parents are away at work.
Many elementary school principals and teachers have always known the "latchkey" child or the "eight-hour orphan." [New York State Teachers Association, "New York State Education," 1944]
The older or simpler device was a latch-string, which could be pulled in to lock up; having it out was symbolic of openness.
knock up (v.): 1660s, "arouse by knocking at the door," from knock (v.) + up (adv.). However it is little used in this sense in American English, where the phrase means "get a woman pregnant" (1813), possibly ultimately from knock in a sense "to copulate with" (1590s; compare slang knocking-shop "brothel," 1860).
Knocked up in the United States, amongst females, the phrase is equivalent to being enciente, so that Englishmen often unconsciously commit themselves when amongst our Yankee cousins. [John Camden Hotten, "The Slang Dictionary," London, 1860]
gate (n.): "opening, entrance," Old English geat (plural geatu) "gate, door, opening, passage, hinged framework barrier," from Proto-Germanic *gatan (source also of Old Norse gat "opening, passage," Old Saxon gat "eye of a needle, hole," Old Frisian gat "hole, opening," Dutch gat "gap, hole, breach," German Gasse "street, lane, alley"), of unknown origin. Meaning "money collected from selling tickets" dates from 1896 (short for gate money, 1820). Gate-crasher is from 1926 as "uninvited party guest;" 1925 in reference to motorists who run railway gates. Finnish katu, Lettish gatua "street" are Germanic loan-words.