buck (n.1)
"male deer," c.1300, earlier "male goat;" from Old English bucca "male goat," from Proto-Germanic *bukkon (cognates: Old Saxon buck, Middle Dutch boc, Dutch bok, Old High German boc, German Bock, Old Norse bokkr), perhaps from a PIE root *bhugo (cognates: 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.
buck (v.)
1848, apparently with a sense of "jump like a buck," from buck (n.1). Related: Bucked; bucking. Buck up "cheer up" is from 1844.
buck (n.2)
"sawhorse," 1817, American English, apparently from Dutch bok "trestle."