Online Etymology Dictionary

portentous (adj.): 1540s, from Latin portentosus "monstrous, marvelous, threatening," from portentem "portent" (see portend). Related: Portentously.
porter (n.1): "person who carries," late 14c. (mid-13c. as a surname), from Anglo-French portour, Old French porteor "porter, bearer; reporter" (12c.), from Late Latin portatorem (nominative portator) "carrier, one who carries," from past participle stem of Latin portare "to carry" (see port (n.1)).
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)).
porter (n.3): type of dark beer, 1734, short for porter's ale (1721), from porter (n.1), because the beer was made for or preferred by porters and other laborers, being cheap and strong.
porterhouse (n.): also porter-house, "restaurant or chophouse where porter is served," 1754, from porter (n.3) + house (n.). Porterhouse steak (1841) is said to be from a particular establishment in New York City.
portfolio (n.): 1722, porto folio; 1719 as port folio, from Italian portafoglio "a case for carrying loose papers," from porta, imperative of portare "to carry" (see port (n.1)) + foglio "sheet, leaf," from Latin folium (see folio). Meaning "official documents of a state department" is from 1835. A minister without portfolio is one not in charge of a particular department. Meaning "collection of securities held" is from 1930; portfolio investment is from 1955.
porthole (n.): also port-hole, 1590s, from port (n.2) + hole (n.).
portico (n.): c. 1600, from Italian portico, from Latin porticus "colonnade, arcade, covered walk, porch," from porta "gate" (see port (n.1)). Especially of the Painted Porch in Athens.
portiere (n.): door curtain, 1843, from French portière, from Medieval Latin portaria, fem. singular of Latin portarius "belonging to a door or gate" (see porter (n.2)).
portion (n.): early 14c., "allotted part, share," from Old French porcion "part, portion" (12c., Modern French portion) and directly from Latin portionem (nominative portio) "share, part," accusative of the noun in the phrase pro portione "according to the relation (of parts to each other)" (see proportion). From late 14c. in general sense of "section into which something is divided."
portion (v.): "to divide in portions," early 14c., from Old French porcioner "share out, divide in portions," from porcion (see portion (n.)). Related: Portioned; portioning.
Portland: in Portland cement, 1720, named by its inventor, English mason Joseph Aspdin, from resemblance of the color to the stone of Portland peninsula on the coast of Dorsetshire. The place name is literally "land surrounding a harbor," Old English Portlanda. Portland, Maine, U.S.A., took its name 1786, for the place in England. Portland, Oregon, was said to have been named for the city in Maine, which won the honor by a coin toss over Boston.
portly (adj.): early 15c., "stately, dignified," from port (n.3) "bearing, carriage" + -ly (1). Meaning "stout" is first recorded 1590s.
portmanteau (n.): 1580s, "traveling case or bag for clothes and other necessaries," from Middle French portemanteau "traveling bag," originally "court official who carried a prince's mantle" (1540s), from porte, imperative of porter "to carry" (see porter (n.1)) + manteau "cloak" (see mantle (n.)).

Portmanteau word "word blending the sound of two different words" (1882), coined by "Lewis Carroll" (Charles L. Dodgson, 1832-1898) for the sort of words he invented for "Jabberwocky," on notion of "two meanings packed up into one word." As a noun in this sense from 1872.
portobello: type of mushroom, by 1986, no agreed-upon theory accounts for the name, which seems to be a marketing coinage. London's Portobello Road (one suggested source of the mushroom name) originally was the lane to Porto Bello House, named for the Panamanian place captured by the British under Vernon in 1739.
portrait (n.): 1560s, "a figure, drawn or painted," a back formation from portraiture or directly from Middle French portrait, from Old French portret (13c.), noun use of past participle of portraire "to paint, depict" (see portray). Especially of the head and face of a person.
portraiture (n.): mid-14c., from Old French portraiture "portrait, image, portrayal, resemblance" (12c.), from portrait (see portrait).
portray (v.): mid-13c., "to draw, paint" (something), from Anglo-French purtraire, Old French portraire "to draw, to paint, portray" (12c.), literally "trace, draw forth," from por- "forth" (from Latin pro-; see pro-) + traire "trace, draw," from Latin trahere "to drag, draw" (see tract (n.1)). Meaning "depict in words, describe" is from late 14c. Related: Portrayed; portraying.
portrayal (n.): 1834, from portray + -al (2). The idea formerly was expressed by portray (n.), 1610s.
portsider (n.): "left-handed person," 1913, American English baseball slang, from port (n.1) in the nautical sense + side (n.).
Portugal: late 14c., Portyngale, from Medieval Latin Portus Cale (Roman name of modern Oporto), "the port of Gaya," from Latin portus "harbor, port" (see port (n.1)). Alfonso, Count of Portucale, became the first king of Portugal.
Portuguese (n.): 1610s, the language, or a resident, of Portugal; 1660s as an adjective, from Portuguese Portuguez (see Portugal + -ese). The ending was vulgarly mistaken for a plural in English, and false singular Portugee (1830) was formed (compare Chinee from Chinese). For Portuguese man-of-war, see man-of-war.
posable (adj.): 1972 of questions; 1975 of action figures; from pose (v.1 and 2) + -able.
posada (n.): "inn," 1763, from Spanish posada "home, lodging," from posar "to repose, rest, lodge," from Latin pausare "to cease, lay down" (see pause (n.)).
pose (v.1): late 14c., posen, "suggest (something is so), suppose, assume; grant, concede," from Old French poser "put, place, propose," a term in debating, from Late Latin pausare "to halt, rest, cease, pause" (source also of Italian posare, Spanish posar; see pause (v.)). The Late Latin verb also had a transitive sense, "cause to pause or rest," and hence the Old French verb (in common with cognates in Spanish, Italian, Portuguese) acquired the sense of Latin ponere (past participle positus) "to put, place," by confusion of the similar stems. Meaning "put in a certain position" in English is from early 15c. Sense of "assume a certain attitude" is from 1840; the transitive sense (as an artist's model, etc.) is from 1859. Related: Posed; posing.
One of the most remarkable facts in F[rench] etymology is the extraordinary substitution whereby the Low Lat. pausare came to mean 'to make to rest, to set,' and so usurped the place of the Lat. ponere, to place, set, with which it has no etymological connection. And this it did so effectually as to restrict the F. pondre, the true equivalent of Lat. ponere, to the sense of 'laying eggs;' whilst in all compounds it completely thrust it aside, so that compausare (i.e. F. composer) took the place of Lat. componere, and so on throughout. Hence the extraordinary result, that whilst the E. verbs compose, depose, impose, propose, &c. exactly represent in sense the Lat. componere, deponere, imponere, proponere, &c., we cannot derive the E. verbs from the Lat. ones since they have (as was said) no real etymological connection. [W.W. Skeat, "Etymological Dictionary of the English Language," 1898]
pose (v.2): "to puzzle, confuse, perplex," 1590s, earlier "question, interrogate" (1520s), probably from Middle French poser "suppose, assume," from Old French poser "to put, place, set" (see pose (v.1)). Also in some cases a shortening of English appose "examine closely," and oppose. Related: Posed; posing.
pose (n.): "act of posing the body," 1818, from pose (v.1), in a sense developed in the French cognate. Figuratively from 1884.
Poseidon (n.): Greek god of the sea and earthquakes, Greek Poseidon (Doric Poteidan), of uncertain origin.
poser (n.): "one who practices an affected attitude," 1881, agent noun from pose (v.1); revived in teen-ager slang by 1983. Meaning "question that puzzles" is from 1793 from pose (v.2); earlier it meant "one who asks testing questions" (1580s).
poseur (n.): "one who practices affected attitudes," 1866, from French poseur, from verb poser "affect an attitude or pose," from Old French poser "to put, place, set" (see pose (v.1)). The word is English poser in French garb, and thus could itself be considered an affectation.
posh (adj.): by 1914 (1903 as push), of uncertain origin; no evidence for the common derivation from an acronym of port outward, starboard home, supposedly the shipboard accommodations of wealthy British traveling to India on the P & O Lines (to keep their cabins out of the sun); as per OED, see objections outlined in G. Chowdharay-Best, "Mariner's Mirror," Jan. 1971; also see here. The acronym story dates from 1955. More likely from slang posh "a dandy" (1890), from thieves' slang meaning "money" (1830), originally "coin of small value, halfpenny," possibly from Romany posh "half" [Barnhart].
The cavalryman, far more than the infantryman, makes a point of wearing "posh" clothing on every possible occasion -- "posh" being a term used to designate superior clothing, or articles of attire other than those issued by and strictly conforming to the regulations. [E. Charles Vivian, "The British Army From Within," London, 1914]
posit (v.): "to assert," 1690s, from Latin positus "placed, situated, standing, planted," past participle of ponere "put, place" (see position (n.)). Related: Posited; positing.
position (n.): late 14c., as a term in logic and philosophy, from Old French posicion "position, supposition" (Modern French position), from Latin positionem (nominative positio) "act or fact of placing, situation, position, affirmation," noun of state from past participle stem of ponere "put, place," from PIE *po-s(i)nere, from *apo- "off, away" (see apo-) + *sinere "to leave, let" (see site).

Meaning "proper place occupied by a person or thing" is from 1540s. Meaning "manner in which some physical thing is arranged or posed" first recorded 1703; specifically in reference to dance steps, 1778, sexual intercourse, 1883. Meaning "official station, employment" is from 1890.
position (v.): 1670s, "to assume a position (intransitive), from position (n.). Transitive sense of "to put in a particular position" is recorded from 1817. Related: Positioned; positioning.
positional (adj.): 1570s, from position (n.) + -al (1).
positive (adj.): early 14c., originally a legal term meaning "formally laid down," from Old French positif (13c.) and directly from Latin positivus "settled by agreement, positive" (opposed to naturalis "natural"), from positus, past participle of ponere "put, place" (see position (n.)).

Sense of "absolute" is from mid-15c. Meaning in philosophy of "dealing only with facts" is from 1590s. Sense broadened to "expressed without qualification" (1590s), then "confident in opinion" (1660s); mathematical use is from 1704; in electricity, 1755. Psychological sense of "concentrating on what is constructive and good" is recorded from 1916.
positive (n.): 1520s, from positive (adj.).
positively (adv.): mid-15c., "in a definite way," from positive (adj.) + -ly (2). Meaning "absolutely" is from 1777.
positivism (n.): 1847, the philosophy of Auguste Comte (1798-1857), who published "Philosophie positive" in 1830; see positive (adj.) in the "just the facts" sense + -ism. Related: Positivist; Positivistic.
positivity (n.): 1650s, from positive (adj.) + -ity.
positron (n.): 1933, coined from posi(tive) (elec)tron.
posse (n.): 1640s (in Anglo-Latin from early 14c.), shortening of posse comitatus "the force of the county" (1620s, in Anglo-Latin from late 13c.), from Medieval Latin posse "body of men, power," from Latin posse "have power, be able" (see potent) + comitatus "of the county," genitive of Late Latin word for "court palace" (see comitatus). Modern slang meaning "small gang" is probably from Western movies.
possess (v.): late 14c., "to hold, occupy, reside in" (without regard to ownership), a back formation from possession and in part from Old French possesser "to have and hold, take, be in possession of" (mid-13c.), from Latin possess-, past participle stem of possidere "to have and hold, possess, be master of, own," from posse "to be able," from potis "able, powerful" (see potent) + esse "to be" (see be). Meaning "to hold as property" is recorded from c. 1500. Demonic sense is recorded from 1530s (implied in possessed). Related: Possessed; possessing.
possessed (adj.): "controlled by an indwelling demon," 1530s, past participle adjective from possess (v.).
possession (n.): mid-14c., "act or fact of possessing, a taking possession, occupation," also "thing possessed, that which is possessed," from Old French possession "fact of having and holding; what is possessed;" also "demonic possession," and directly from Latin possessionem (nominative possessio), noun of action from past participle stem of possidere "to possess" (see possess). Legal property sense is earliest; demonic sense first recorded 1580s. Phrase possession is nine (or eleven) points of the law is out of a supposed 10 (or 12). With eleven from 1640s; with nine from 1690s.
St. Jerome in his 'Life of St. Hilarion' has given us a graphic account of the courage with which that saint confronted, and the success with which he relieved, a possessed camel. [Lecky, "History of European Morals"]
possessive (adj.): mid-15c. (grammatical, also as a noun); 1550s in general use, from Middle French possessif (15c.) "relating to possession, possessive," and directly from Latin possessivus, from possess-, past participle stem of possidere "to possess" (see possess). Related: Possessively; possessiveness.
posset (n.): spiced drink of hot milk and liquor, mid-15c., of unknown origin.
possibility (n.): late 14c., "condition of being possible," from Old French possibilité (13c.) and directly from Latin possibilitatem (nom. possibilitas) "possibility," from possibilis (see possible (adj.)). Meaning "a possible thing or substance" is from c. 1400. Related: Possibilities.
possible (adj.): mid-14c., from Old French possible and directly from Latin possibilis "that can be done," from posse "be able" (see potent).
possible (n.): 1640s, from possible (adj.).