On the American frontier in the mid-to-late 1700s, deer hides were especially valuable. However, they were also common enough to be used in lieu of currency, as a medium of exchange where one high-quality skin equaled one dollar. It is for this reason- the adoption of buckskins as a bartering tool equivalent to US currency- that we began using the word buck as slang for "dollar". The phrase pass the buck (meaning "to shift responsibility") dates back to the 1860s, when card players would use a marker made out of buckskin to indicate whose turn it was to deal. This prompted Truman to say the buck stops here in 1952, giving us that phrase. Now, the word buck itself comes from the Old English word bucca, which actually referred to male goats, and only got applied to deer later. This, through Proto-Germanic bukkon, comes from the Proto-Indo-European reconstruction bhugo, with the same meaning.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.