To refer to legs as gams has always been slang, and is now distinctly dated slang at that. But as usual, there’s more going on with the word than you might have realized. The Late Latin gamba meaning “leg of an animal” is responsible for a whole host of English words.
gams - not technically a plurale tantum, the word is nevertheless almost always heard in the plural. It dates from about 1780 and may derive from the heraldry term gamb, for the leg of an animal used as a charge on a coat of arms. On the other hand, it may instead derive from underworld argot, from Italian. Either way, it comes ultimately from the Latin. I’m not sure when it shifted to its modern (relatively speaking!) American usage of applying specifically to “the shapely legs of a pretty woman.”
gammon - ham or haunch of pork, this one is quite obviously and directly derived from Latin gamba, by way of Old French. (Compare, too, French jambon and Spanish jamon.)
gambol - (1580s) to skip about merrily. This comes by way of French for “the leap of a horse,” and obviously involves kicking and prancing with the legs.
gambit - originally a specific opening in chess, it came in the 1650s (by way of Spanish and then French) from Italian meaning “tripping up.” By the 1850s it had broadened its meaning to any “opening move meant to gain advantage.”
jamb - (early 14th c) the side-piece of the frame of a door or window. Think of the door jambs as being the legs on which the lintel stands.
gambrel roof - (1760s) aka hipped roof, from the idea that its angle is shaped like a horse’s hock.
viola da gamba - (1724 from Italian), literally “viol for the leg,” since it’s held between the legs like a cello.
game - (1780s, originally north Midlands dialect) lame. The etymology of this one is not certain, but one possibility is that it derives from the same gamba root, in which case that game leg seems quite redundant!
So now you know, and can appreciate the great gams that show up all around you… but you should probably refrain from catcalling them, whether they’re on your breakfast plate, framing your door, or under a woman’s skirt. No need to be disrespectful, despite your enthusiasm.
[Pictures: Beauty Parade, cover painting by Billy DeVorss, March 1944 (Image from DTA Collectibles);
Gamboling Lambs, woodblock print by Matt Underwood (Image from his Etsy shop mattunderwood).]