If you wanted to say “five bucks” in French, could you? Not “five dollars,” but something more informal like “five bucks.”
Here’s an example:
J’ai dépensé cinq piasses.
I spent five bucks.
Une piasse is more or less on the same level of informality as “buck” in English. Piasse is only used informally. Dollar is used at all language levels.
Piasse comes from an informal pronunciation of piastre.
[This entry was inspired by the character Louis in Les Parent, “Blues d’automne,” season 3, episode 7, Radio-Canada, Montreal, 25 October 2010. Here, he said he would give his son cinq piasses.]