"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:
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.