There is speculation in straightdope.com that the word “buck” was used in poker games where a token was placed in front of the dealer, and the token was often a knife made of buck horn. It was said, perhaps tongue in cheek, that when it came time for the dealer to surrender the duty to the next player “the buck was passed.” It is plausible that the term was short for buckskin, which was a common medium of exchange. It was written in 1748 that a cask of whiskey was sold to Indians for 5 bucks. “The transition to dollars seems only natural.” The term “sawbuck” for the ten dollar bill has no relation. The old ten dollar bills were denominated with the Roman numeral Xs. “The Xs looked like the X-shaped arms of benches sawyers used to hold up logs for cutting.”