Etymology
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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.)). Its opposite, overdog, is attested by 1908.

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] 
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hound (n.)

Old English hund "dog," from Proto-Germanic *hundaz (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." Meaning narrowed 12c. to "dog used for hunting" (compare dog (n.)). Contemptuously, of a man, from late Old English.

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doggerel (n.)

1630s, "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"]. Earlier as an adjective (rim doggerel, late 14c.), an epithet applied to loose, irregular verse in burlesque poetry.

Probably from pejorative suffix -rel + dog (n.), but the sense connection is not obvious. Perhaps it was applied to bad poetry with a suggestion of puppyish clumsiness, or being fit only for dogs, or from the "mean, contemptible" associations of dog in Middle English. Attested as a surname from late 13c., but the sense is not evident. Related: Doggerelist.

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doggy (n.)

also doggie, "a little dog, a pet word for a dog," 1825, from dog (n.) + -y (3). Doggy-bag "bag provided by restaurants for customers to take home leftovers" (presumably to feed to the dog) is attested by 1962.

LIVING IT UP. Marveling at size of sirloin steaks, Dave and Betty celebrate $4-a-week raise at a restaurant dinner. They paid $3.50 each, left with enough uneaten steak in a "doggie bag" to feed themselves, not the dog, all next day. [Life magazine, photo caption from article on living economically, April 6, 1962]

As an adj. doggy is attested from late 14c., from -y (2). The word has been used in various formations at least since late 19c. to describe the rear-entry variant of the human sex act when one partner is on all fours.

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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.
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dogfish (n.)

a name for various types of small shark, mid-15c., dogge fysch, from dog (n.) + fish (n.). It is said to be so called because it hunts in packs. The wild dog was the image of sharks in classical antiquity as well, and Greek used kyon "dog" also for dogfish and sharks, especially the smaller kind.

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.]

Greek galeos "dogfish or shark" perhaps is based on galen "weasel, marten," which also was a fish name.

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pig (n.1)

Middle English pigge "a young pig" (mid-13c., late 12c. as a surname), probably from Old English *picg, found in compounds, but, like dog, its further etymology unknown. The older general word for adults was swine, if female, sow, if male, boar. Apparently related to Low German bigge, Dutch big ("but the phonology is difficult" -- OED).

By early 14c. pig was used of a swine or hog regardless of age or sex. Applied to persons, usually in contempt, since 1540s; the derogatory meaning "police officer" has been in underworld slang at least since 1811.

The pigs frisked my panney, and nailed my screws; the officers searched my house, and seized my picklock keys. ["Dictionary of Buckish Slang, University Wit and Pickpocket Eloquence," London, 1811]

Another Old English word for the animal was fearh, which is related to furh "furrow," from PIE *perk- "dig, furrow" (source also of Latin porcus "pig," see pork). "This reflects a widespread IE tendency to name animals from typical attributes or activities" [Lass].

Synonyms grunter, porker are from sailors' and fishermen's euphemistic avoidance of uttering the word pig at sea, a superstition perhaps based on the fate of the Gadarene swine, who drowned. The image of a pig in a poke is attested from late 14c. (see poke (n.1)). Flying pigs as a type of something unreal is from 1610s.

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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 and dag (v.) "to pierce or stab" (1630s, perhaps 15c.).

The trees have hard, white wood that was said to have been used in making butchers' skewers; another name for it was skewer-wood. This explanation is as old as the word itself in English, but the form *dagwood is not attested. Another guess is that the tree was given the name in reference to its fruit, which was called dogberry from 1550s, and dog (n.) had implications of "cheap, inferior" (i.e. "fit for a dog").

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canivorous (adj.)
"dog-eating," 1835, from Latin canis "dog" (from PIE root *kwon- "dog") + -vorous "eating, devouring."
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canine (n.)
late 14c., "a pointed tooth," from Latin caninus "of the dog," genitive of canis "dog" (source of Italian cane, French chien), from PIE root *kwon- "dog." The meaning "a dog" is first recorded 1869.
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