Gams is an obsolete slang term for legs, the kind of thing that a gumshoe would come out with. “She had gams that went all the way up to the top … and all the way back down again. They were the kind of gams that could drive a man to drink, and she didn’t even have a licence for them…”
According to the liar Daniel Cassidy in his lying piece of trash How The Irish Invented Slang, this is Irish. Of course it is. According to Cassidy, half the words in the English language had an Irish origin lurking behind them, usually a dodgy-looking piece of work with a Noo Yoik accent which no Irish-speaker would recognise. In this case, Cassidy’s candidate is gamba, which means a lump or a chunk.
There is some doubt about the immediate origin of gams, but there is no doubt that it comes from a Romance (i.e. a Latin root) word which means leg. There are many related words. The word camba in Catalan, jambe in French (gamba in Old French), gamba in Spanish (which means the bottom part of an animal’s leg as well as a prawn). At some point, probably in the Middle Ages, the French word was borrowed into Irish as gamba, meaning a lump. As I have said before, when an Irish noun ends in an –a, it is usually a sure sign that it is a borrowing from another language (siopa, pota, cóta, cárta, nóta.) In other words, the slang word gam comes from French or Italian, and the Irish word gamba comes from the same root. But there is no evidence that Irish had anything directly to do with the English slang word gam.
Incidentally, the word gaimbín means a little piece or (financial) interest in Irish, and a gombeen-man in Irish English means a loan-shark. My wife’s family use gombeen in English to mean an idiot as well, probably because it sounds right, like goof or geek or dork. I had always assumed that gaimbín was simply a diminutive form of gamba but apparently the situation is more complex than that:
You learn something new every day, if you keep an open mind and listen to the experts.