buck-tooth n.

"male deer," c. 1300, earlier "male goat;" from Old English bucca "male goat," from Proto-Germanic *bukkon (source also of Old Saxon buck, Middle Dutch boc, Dutch bok, Old High German boc, German Bock, Old Norse bokkr), perhaps from a PIE root *bhugo (source also of Avestan buza "buck, goat," Armenian buc "lamb"), but some speculate that it is from a lost pre-Germanic language. Barnhart says Old English buc "male deer," listed in some sources, is a "ghost word or scribal error." The Germanic word (in the sense "he-goat") was borrowed in French as bouc.

The meaning "a man" is from c. 1300 (Old Norse bokki also was used in this sense). Especially "fashionable man" (1725); also used of a male Native American (c. 1800) or Negro (1835). This also is perhaps the sense in army slang buck private "private of the lowest class" (1870s).

The phrase pass the buck is recorded in the literal sense 1865, American English poker slang; the buck in question being originally perhaps a buckhorn-handled knife:

The 'buck' is any inanimate object, usually [a] knife or pencil, which is thrown into a jack pot and temporarily taken by the winner of the pot. Whenever the deal reaches the holder of the 'buck', a new jack pot must be made. [J.W. Keller, "Draw Poker," 1887]

The figurative sense of "shift responsibility" is first recorded 1912; the phrase the buck stops here (1952) is associated with U.S. President Harry Truman.

Old English toð (plural teð), from Proto-Germanic *tanthu- (source also of Old Saxon, Danish, Swedish, Dutch tand, Old Norse tönn, Old Frisian toth, Old High German zand, German Zahn, Gothic tunþus), from PIE root *dent- "tooth." Plural teeth is an instance of i-mutation.

The loss of -n- before spirants is regular in Old English, Old Frisian, and Old Saxon: compare goose (n.), five, mouth (n.). Also thought, from stem of think; couth from the stem of can (v.1); us from *uns.

Application to tooth-like parts of other objects (saws, combs, etc.) first recorded 1520s. Tooth and nail as weapons is from 1530s. The tooth-fairy is attested from 1964.