Online Etymology Dictionary

dog (v.): "to track like a dog," 1510s, see dog (n.). Related: Dogged; dogging.
dog (n.): Old English docga, a late, rare word, used in at least one Middle English source in reference to a powerful breed of canine. The word forced out Old English hund (the general Germanic and Indo-European word; see canine) by 16c. and subsequently was picked up in many continental languages (French dogue (16c.), Danish dogge, German Dogge (16c.)), but the origin remains one of the great mysteries of English etymology.

Many expressions -- a dog's life (c. 1600), go to the dogs (1610s), etc. -- reflect earlier hard use of the animals as hunting accessories, not pampered pets. In ancient times, "the dog" was the worst throw in dice (attested in Greek, Latin, and Sanskrit, where the word for "the lucky player" was literally "the dog-killer"), which plausibly explains the Greek word for "danger," kindynas, which appears to be "play the dog."

Slang meaning "ugly woman" is from 1930s; that of "sexually aggressive man" is from 1950s. Adjectival phrase dog-eat-dog attested by 1850s. Dog tag is from 1918. To dog-ear a book is from 1650s; dog-eared in extended sense of "worn, unkempt" is from 1894.
Notwithstanding, as a dog hath a day, so may I perchance have time to declare it in deeds. [Princess Elizabeth, 1550]
Phrase put on the dog "get dressed up" (1934) may look back to the stiff stand-up shirt collars that in the 1890s were the height of male fashion (and were known as dog-collars at least from 1883), with reference to collars worn by dogs. The common Spanish word for "dog," perro, also is a mystery word of unknown origin, perhaps from Iberian. A group of Slavic "dog" words (Old Church Slavonic pisu, Polish pies, Serbo-Croatian pas) likewise are of unknown origin.
hot dog (n.): also hotdog, "sausage on a split roll," c. 1890, American English, from hot (adj.) + dog (n.). Many early references are in college student publications; later popularized, but probably not coined, by cartoonist T.A. "Tad" Dorgan (1877-1929). It is said in early explanations to echo a suspicion (occasionally justified) that sausages contained dog meat.

Meaning "someone particularly skilled or excellent" (with overtones of showing off) is from 1896. Connection between the two senses, if any, is unclear. Hot dog! as an exclamation of approval was in use by 1906.
hot-dog, n. 1. One very proficient in certain things. 2. A hot sausage. 3. A hard student. 4. A conceited person. ["College Words and Phrases," in "Dialect Notes," 1900]
Related: Hot-dogger; hot-dogging.
sheep-dog (n.): 1774, from sheep (n.) + dog (n.).
hound-dog (n.): by 1821, from hound (n.) + dog (n.).
sea-dog (n.): 1590s, "harbor seal," from sea + dog (n.). Also "pirate" (1650s). Meaning "old seaman, sailor who has been long afloat" is attested from 1840.
moon-dog (n.): one who bays at the moon, 1660s, from moon (n.) + dog (n.). Earlier in same sense was mooner (1570s).
hang-dog (adj.): also hangdog, 1670s, apparently "befitting a hang-dog," that is, a despicable, degraded fellow, so called either from being fit only to hang a dog (with construction as in cutthroat, daredevil) or of being a low person (i.e. dog) fit only for hanging. The noun, however, is attested only from 1680s.
dog days (n.): 1530s, from Latin dies caniculares, from Greek; so called because they occur around the time of the heliacal rising of Sirius, the Dog Star (kyon seirios). Noted as the hottest and most unwholesome time of the year; usually July 3 to Aug. 11, but variously calculated, depending on latitude and on whether the greater Dog-star (Sirius) or the lesser one (Procyon) is reckoned.

The heliacal rising of Sirius has shifted down the calendar with the precession of the equinoxes; in ancient Egypt c. 3000 B.C.E. it coincided with the summer solstice, which also was the new year and the beginning of the inundation of the Nile. The "dog" association apparently began here (the star's hieroglyph was a dog), but the reasons for it are obscure.
dog leg (n.): "something bent like a dog's hind leg," 1703. Originally of a type of staircase.
dogged (adj.): "having the qualities of a dog" (mostly in a negative sense), c. 1300, from dog (n.). Meaning "persistent" is from 1779. Hence doggedly (late 14c.), "cruelly, maliciously;" later "with a dog's persistence" (1773). Related: Doggedness.
dogfish (n.): a name for various types of small shark, late 15c., dokefyche, from dog (n.) + fish (n.). Said to be so called because they hunt in packs. This was the image of sharks in classical antiquity as well.
But in the Mediterranean, among the Greeks and Romans of antiquity, closer contact with sharks had left an impression of vicious dogs of the sea. Thus, Pliny's canis marinus. The metaphor of the dog spread to the North to dominate the European image of the shark, from the Italian pescecane and French chien de mer to the German Meerhund and Hundfisch and English sea dog and dogfish. [Tom Jones, "The Xoc, the Sharke and the Sea Dogs," in "Fifth Palenque Round Table, 1983," edited by Virginia M. Field, 1985.]
doghouse (n.): 1610s, from dog (n.) + house (n.). Originally a kennel; the backyard type, for a single animal, is late 19c. Figurative sense of "disgrace" is from 1932.
dogfight (n.): "aerial combat," World War I air forces slang, from earlier meaning "riotous brawl" (1880s); from dog (n.) + fight (n.). The literal sense of "a fight among or between dogs" is from 1650s.
doggerel: late 14c. (adj.); 1630s (n.), "Any rhyming verse in which the meter is forced into metronomic regularity by the stressing of normally unstressed syllables and in which rhyme is forced or banal" [Miller Williams, "Patterns of Poetry"]. probably from dog (n.) + pejorative suffix -rel and applied to bad poetry perhaps with a suggestion of puppyish clumsiness, or being fit only for dogs. Attested as a surname from mid-13c., but the sense is not evident.
doggy (n.): also doggie, 1825, from dog (n.) + -y (3). Doggy-bag attested from 1965. As an adj. doggy is attested from late 14c., from -y (2). The word has been used in various formations since at least late 19c. to describe the sex act when one partner is on all fours.
dogwood (n.): shrubs and small trees of the genus Cornus, 1610s, earlier dog-tree (1540s); the first element sometimes said to have been perhaps dag -- compare dagger, dag (v.) "to pierce or stab" (1630s, perhaps 15c.) -- the trees have hard, white wood that was used in making skewers; another name for it was skewer-wood. But another guess is that the tree was given the name in reference to its fruit, which was called dogberry from 1550s, and dog had implications of "cheap, inferior" (i.e. "fit for a dog").
watchdog (n.): also watch-dog, c. 1600, from watch (v.) + dog (n.). Figurative sense is attested by 1845.
doggone (adj.): 1851, American English, a "fantastic perversion of god-damned" [Weekley]. But Mencken favors the theory that it is "a blend form of dog on it; in fact it is still often used with it following. It is thus a brother to the old English phrase, 'a pox upon it,' but is considerably more decorous."
lapdog (n.): also lap-dog, 1640s, "small dog fondled in the lap," from lap (n.1) + dog (n.); figurative sense of "subservient person" is by 1950.
Senator McCarthy (R-Wis) renewed his Communists-in-Government charges today and called Senator Tydings (D-Md) the Truman administration's "whimpering lap dog." [AP news story, Aug. 7, 1950]
dawg (n.): colloquial for dog, attested from 1898.
underdog (n.): "the beaten dog in a fight," 1887, from under + dog (n.). Compare top dog "dominant person in a situation or hierarchy" (see top (adj.)).
I'm a poor underdog
But tonight I will bark
With the great Overdog
That romps through the dark.

[from "Canis Major," Robert Frost, 1928]
Sirius (n.): brightest star by magnitude, late 14c., from Latin Sirius "the Dog Star," from Greek Seirios, said to mean literally "scorching" or "the scorcher." But other related Greek words seem to derive from this use, and the name might be a folk-etymologized borrowing from some other language. An Egyptian name for it was Sothis. The connection of the star with scorching heat is from its ancient heliacal rising at the summer solstice (see dog days). Also see dog star. Related: Sirian. The constellation Canis Major seems to have grown from the star, not the other way.
Homer made much of it as [Kyon], but his Dog doubtless was limited to the star Sirius, as among the ancients generally till, at some unknown date, the constellation was formed as we have it, -- indeed till long afterwards, for we find many allusions to the Dog in which we are uncertain whether the constellation or its lucida is referred to. [Richard Hinckley Allen, Canis Major in "Star Names and Their Meanings," London: 1899]
hound (n.): Old English hund "dog," from Proto-Germanic *hundas (source also of Old Saxon and Old Frisian hund, Old High German hunt, German Hund, Old Norse hundr, Gothic hunds), from PIE *kwnto-, dental enlargement of root *kwon- "dog" (see canine). Meaning narrowed 12c. to "dog used for hunting" (compare dog (n.)). Contemptuously, of a man, from late Old English.
bulldog (n.): c. 1500, from bull (n.1) + dog (n.). Perhaps from shape, perhaps because originally used for baiting bulls.
horndog (n.): by 1995, from horn (n.) in the sexual sense (see horny) + dog (n.).
shrewd (adj.): c. 1300, "wicked, evil," from shrewe "wicked man" (see shrew). Compare crabbed from crab (n.), dogged from dog (n.), wicked from witch (n.). The sense of "cunning" is first recorded 1510s. Related: Shrewdly; shrewdness. Strutt's "Sports and Pastimes of the People of England" (1801) has a shrewdness of apes for a company or group of them. Shrewdie "cunning person" is from 1916.
seeing (adj.): c. 1300, present participle adjective from see (v.). Seeing Eye dog first attested 1929, American English, trademarked by Seeing Eye Inc. of New Jersey.
pug (n.): 1560s, general term of endearment (also puggy), probably related to puck (n.2); one of the earliest senses is "sprite, imp" (1610s). The sense of "miniature dog" is from 1749 (pug-dog); that of "monkey" is 1660s. The word at various times meant "a bargeman" (1590s), "a harlot" (c. 1600), and "an upper servant in a great house" (1847).
heel-tap (n.): also heeltap, 1680s, "one of the bits of leather that are stacked up to make a shoe heel" (see heel (n.1)); meaning "bit of liquor left in a glass or bottle" first recorded 1767; the exact connection is uncertain unless it be "the last or final part." Related: Heeltaps.
A jolly dog, is one who has no conversation in company, but "fill about, what's the toast, damn your heel-taps," and roars out an obscene ballad when he gets drunk. ["The Batchelor," March 28, 1767]
pup (n.): "young dog," 1760, shortened form of puppy (q.v.). Used from 1580s for "conceited person." Applied to the young of the fur seal from 1815. Used for "inexperienced person" by 1890. Pup tent (also dog tent) is from 1863. Sopwith pup, popular name of the Sopwith Scout Tractor airplane, is from 1917.
veterinarian (n.): animal doctor, 1640s, from Latin veterinarius "of or having to do with beasts of burden," also, as a noun, "cattle doctor," from veterinum "beast of burden," perhaps from vetus (genitive veteris) "old" (see veteran), possibly from the notion of "experienced," or of "one year old" (hence strong enough to draw burdens). Another theory connects it to Latin vehere "to draw," on notion of "used as a draft animal." Replaced native dog-leech (1520s).
guide (n.): mid-14c., "one who shows the way," from Old French guide, 14c., verbal noun from guider (see guide (v.)). In book titles from 1610s; meaning "book of information on local sites" is from 1759. In 18c. France, a "for Dummies" or "Idiot's Guide to" book would have been a guid' âne, literally "guide-ass." Guide-dog for the blind is from 1932.
running (adj.): present participle adjective from run (v.). Running mate originally was a horse entered in a race to set the pace for another from the same stable who was intended to win (1865); U.S. vice-presidential sense is recorded from 1888. Running dog first recorded 1937, from Chinese and North Korean communist phrases used to describe supposed imperialist lackeys, such as Mandarin zou gou "running dog," on the notion of a dog that runs at its master's command. Running board first attested 1817, in reference to ships and boats; 1907 of cars and trucks.
shaggy (adj.): "rough, coarse, unkempt," 1590s, from shag (n.) + -y (2). Related: Shaggily; shagginess. Earlier was shagged, from Old English sceacgede "hairy;" compare Old Norse skeggjaðr, Danish skægget "bearded." The shaggy-dog story as a type of joke is attested from 1944, perhaps from vaudeville.
puppy (n.): late 15c., "woman's small pet dog," of uncertain origin but likely from Middle French poupée "doll, toy" (see puppet). Meaning shifted from "toy dog" to "young dog" (1590s), replacing Middle English whelp. In early use in English puppet and puppy were not always distinct from each other. Also used about that time in sense of "vain young man." Puppy-dog first attested 1590s (in Shakespeare, puppi-dogges). Puppy love is from 1823. Puppy fat is from 1937.
top (adj.): "being at the top," 1590s, from top (n.1). Top dollar "high price" is from 1942. Top-drawer (1920) is from British expression out of the top drawer "upper-class." Top ten in popular music is from 1945 ("Billboard"). The top dog is the one uppermost in a fight, from 1868 in figurative use, opposed to the underdog.
But if the under dog in the social fight runs away with a bone in violation of superior force, the top dog runs after him bellowing, "Thou shalt not steal," and all the other top dogs unite in bellowing, "This is divine law and not dog law;" the verdict of the top dog so far as law, religion, and other forms of brute force are concerned settles the question. [Van Buren Denslow, "Modern Thinkers: What They Think and Why," 1880]
huff (v.): mid-15c., apparently imitative of forcible exhaling. Extended sense of "to bluster with arrogance or indignation" is attested from 1590s. Related: Huffed; huffing. As a slang term for a type of narcotics abuse, by 1996. Huff cap was 17c. slang for "swaggerer, blusterer" (i.e., one with an inflated head), and was noted in 1577 among the popular terms for "strong beer or ale" (with mad dog and dragon's milk), probably because it goes to the head and huffs one's cap.
German (adj.): "of or pertaining to Germany or the Germans," 1550s, from German (n.). German shepherd as a breed of dog (1922) is short for German shepherd dog (1889), which translates German deutscher Schäferhund. German Ocean as an old name for the North Sea translates Ptolemy. German measles attested by 1856. German-American is from 1880. German Reformed church is from 1812.
prairie (n.): tract of level or undulating grassland in North America, by 1773, from French prairie "meadow, grassland," from Old French praerie "meadow, pastureland" (12c.), from Vulgar Latin *prataria, from Latin pratum "meadow," originally "a hollow." The word existed in Middle English as prayere, but was lost and reborrowed to describe the American plains. Prairie dog is attested from 1774; prairie schooner "immigrant's wagon" is from 1841. Illinois has been the Prairie State since at least 1861. In Latin, Neptunia prata was poetic for "the sea."
apothecary (n.): mid-14c., "shopkeeper, especially one who stores, compounds, and sells medicaments," from Old French apotecaire (13c., Modern French apothicaire), from Late Latin apothecarius "storekeeper," from Latin apotheca "storehouse," from Greek apotheke "barn, storehouse," literally "a place where things are put away," from apo- "away" (see apo-) + tithenai "to put, to place" (see theme). Same root produced French boutique and Spanish bodega. Cognate compounds produced Sanskrit apadha- "concealment," Old Persian apadana- "palace."

Drugs and herbs being among the chief items of non-perishable goods, the meaning narrowed 17c. to "druggist" (Apothecaries' Company of London separated from the Grocers' in 1617). Apothecaries formerly were notorious for "the assumed gravity and affectation of knowledge generally put on by the gentlemen of this profession, who are commonly as superficial in their learning as they are pedantic in their language" [Francis Grose, "A Classical Dictionary of the Vulgar Tongue," 1796]. Hence, Apothecary's Latin, barbarously mangled, also known as Dog Latin.
doge (n.): "chief magistrate of Venice or Genoa," 1540s, from Venetian dialect doge, from Latin ducem, accusative of dux "leader" (see duke (n.)).
dogger (n.): "two-masted fishing boat," used in North Sea fishery, mid-14c., which is of unknown origin. It likely is the source of the name Dogger Bank (1660s) for the great banks of shoals in the North Sea.
dogie (n.): "motherless calf in a herd," 1887, cowboy slang, of uncertain origin.
dogma (n.): c. 1600 (in plural dogmata), from Latin dogma "philosophical tenet," from Greek dogma (genitive dogmatos) "opinion, tenet," literally "that which one thinks is true," from dokein "to seem good, think" (see decent). Treated in 17c.-18c. as a Greek word in English.
dogmatic (adj.): 1670s, from Late Latin dogmaticus, from Greek dogmatikos "pertaining to doctrines," from dogma (see dogma). Related: Dogmatical (c. 1600).
dogs (n.): "feet," 1913, from rhyming slang dog's meat.
dogmatism (n.): c. 1600, but not in common use until 19c., from French dogmatisme (16c.), from Medieval Latin dogmatismus, from Latin dogma (see dogma).
hair (n.): Old English hær "hair, a hair," from Proto-Germanic *khæran (source also of Old Saxon, Old Norse, Old High German har, Old Frisian her, Dutch and German haar "hair"), perhaps from PIE *ghers- "to stand out, to bristle, rise to a point" (source also of Lithuanian serys "bristle;" see horror).

Spelling influenced by Old Norse har and Old English haire "haircloth," from Old French haire, from Frankish *harja or some other Germanic source (see above). Hair-dye is from 1803. To let one's hair down "become familiar" is first recorded 1850. Homeopathic phrase hair of the dog (that bit you), remedy from the same thing that caused the malady, especially a drink on the morning after a debauch, 1540s in English, is in Pliny.
caterpillar (n.): mid-15c., catyrpel, probably altered (by association with Middle English piller "plunderer;" see pillage) from Old North French caterpilose "caterpillar" (Old French chatepelose), literally "shaggy cat" (probably in reference to the "wooly-bear" variety), from Late Latin catta pilosa, from catta "cat" (see cat (n.)) + pilosus "hairy, shaggy, covered with hair," from pilus "hair" (see pile (n.3)). Compare also French chenille "caterpillar," literally "little dog." A Swiss German name for it is teufelskatz "devil's cat." "The caterpillar has in many idioms received the name of other animals" [Kitchin, who cites also Milanese cagnon "little dog," Italian dialectal gattola "little cat," Kentish hop-dog, hop-cat, Portuguese lagarta "lizard." Compare also American English wooly-bear for the hairy variety. An Old English name for it was cawelworm "cole-worm." Caterpillar tractor is from 1908.