Etymology
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dog-leg (adj.)

also dogleg, "bent like a dog's hind leg," 1843, earlier dog-legged (1703), which was used originally of a type of staircase which has no well hole and consists of two flights with or without winders. See dog (n.) + leg (n.).

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sea-dog (n.)

1590s, "harbor seal," from sea + dog (n.). Also "pirate" (1650s). Meaning "old seaman, sailor who has been long afloat" is attested by 1823. In Middle English sea-hound was used of the walrus and the beaver.

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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.

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dawg (n.)
colloquial for dog, attested from 1898.
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watchdog (n.)
also watch-dog, c. 1600, from watch (v.) + dog (n.). Figurative sense is attested by 1845.
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horndog (n.)
by 1995, from horn (n.) in the sexual sense (see horny) + dog (n.).
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dogface (n.)

"soldier in the U.S. Army," especially an infantryman, by 1941, from dog (n.) + face (n.). Said to have been originally a contemptuous name given by the Marines.

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dogged (adj.)

"having the qualities of a dog" (mostly in a negative sense, "mean, surly, contemptible"), c. 1300, from dog (n.). Meaning "persistent, silently obstinate" is from 1779. Hence doggedly (late 14c.), "cruelly, maliciously;" later "with a dog's persistence" (1773). Related: Doggedness.

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dogfight (n.)

also dog-fight, "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 (Middle English had dogg feghttyng, c. 1500).

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doghouse (n.)

also dog-house, "box in the shape of a house for use by dogs," 1610s, from dog (n.) + house (n.). Originally a kennel; application to the backyard type, for a single animal, is from late 19c. Figurative in the doghouse "in temporary disgrace" is by 1932.

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