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"male deer," c.1300, earlier "male goat;" from Old English bucca "male goat," from Proto-Germanic *bukkon (cf. Old Saxon buck, Middle Dutch boc, Dutch bok, Old High German boc, German Bock, Old Norse bokkr), perhaps from a PIE root *bhugo (cf. 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."
Meaning "dollar" is 1856, American English, perhaps an abbreviation of buckskin, a unit of trade among Indians and Europeans in frontier days, attested in this sense from 1748. Pass the buck is first recorded in the literal sense 1865, American English:
The 'buck' is any inanimate object, usually 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]Perhaps originally especially a buck-handled knife. The figurative sense of "shift responsibility" is first recorded 1912. Buck private is recorded by 1870s, of uncertain signification.
"sawhorse," 1817, American English, apparently from Dutch bok "trestle."
1848, apparently with a sense of "jump like a buck," from buck (n.1). Related: Bucked; bucking. Buck up "cheer up" is from 1844.
[all senses ultimately fr buck, ''male animal, usually horned''; the semantics are complex: for example, the first sense is said to be fr the fact that a buck deer's skin was more valuable than a female's skin; the other senses have most to do with male behavior of a butting and strutting sort]