Etymology
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turtle (n.2)
"turtledove," Old English turtle, dissimilation of Latin turtur "turtledove," a reduplicated form imitative of the bird's coo. Graceful, harmonious and affectionate to its mate, hence a term of endearment in Middle English. Turtle-dove is attested from c. 1300.
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loggerhead (n.)

1580s, "stupid person, blockhead, dunce, numbskull," perhaps from dialectal logger "heavy block of wood" + head (n.). Later it meant a type of thick-headed iron tool (1680s), a type of cannon shot, a post in the stern of a whale-boat, and a type of turtle (1650s). Loggerheads "fighting, fisticuffs" is from 1670s, but the exact notion in the compound is uncertain, perhaps it suggests the heavy tool used as a weapon. The phrase at loggerheads "in disagreement" is first recorded 1670s.

[W]e three loggerheads be: a sentence frequently written under two heads, and the reader by repeating it makes himself the third. [Grose, "Dictionary of the Vulgar Tongue," 1785]
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turtle (n.1)
"tortoise," c. 1600, originally "marine tortoise," from French tortue, tortre (13c.) "turtle, tortoise" (often associated with diabolical beasts), of unknown origin. The English word perhaps is a sailors' mauling of the French one, influenced by the similar sounding turtle (n.2). Later extended to land tortoises; sea-turtle is attested from 1610s.
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box-turtle (n.)
1825, American English for what is called by English writers a box-tortoise (1834), from box (n.1), so called for its resemblance to a tight, closed box when the head, tail, and legs are drawn in.
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turtleneck (n.)
also turtle-neck "close-fitting collar," 1893, from turtle (n.1) + neck (n.).
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terrapin (n.)
North American turtle, 1670s, earlier torope (1610s), from an Algonquian source (such as Abenaki turepe, Munsee (Delaware) tolpew "turtle"). Subsequently extended to allied species in South America, East Indies, China, North Africa.
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leather-back (n.)
soft-shelled sea-turtle, 1855, from leather + back (n.). So called for its color.
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ridley 

type of sea-turtle, by 1942, from a common name of the animals in the Florida Keys, but the word is of unknown origin.

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mock (adj.)

prefixed to a noun, "feigned, counterfeit, spurious; having a close (but deceptive) resemblance," 1540s, from mock, verb and noun. Mock-heroic "counterfeiting or burlesquing the heroic style or character" is attested from 1711 (Addison), describing a satirical use of a serious form; mock-turtle "calf's head stewed or baked and dressed to resemble a turtle," is from 1758; as a kind of soup by 1783.

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snapper (n.)
"one who or that which snaps," 1570s, agent noun from snap (v.). Applied to various fishes since 1690s. Slang meaning "vagina" is by 2000. As a short form of snapping turtle (1784) it is recorded from 1872. Snappers "teeth" is attested from 1924.
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