Green’s Dictionary of Slang

1. (US) to chat, to pay a social call; occas. as n. (see cit. 1908).

1849		J.F. Cooper Sea Lions 230: I see no reason why we should not be neighbourly, and ‘gam’ it a little, when we’ve nothing better to do.
1884		G.A. Sala in Illus. London News 19 July 51 col. 2: I suppose that when the friendly skippers gam, they feast on flummadiddle, a dish composed, I am given to understand, of stale bread, pork fat, molasses, cinnamon, allspice, and cloves [F&H].
1898		(con. 1875) F.T. Bullen Cruise of the ‘Cachalot’ 203: We had heard many glowing accounts from visitors, when ‘gamming,’ of the delights of this well-known port of call. [Ibid.] 338: As soon as we came near enough, ‘gamming’ commenced, for all of us were anxious to know how each other had fared.
1906		Harper’s Mag. May 841: The skipper came over with a boat’s crew and gammed with us [DA].
1908		J. Kelley Thirteen Years in Oregon Penitentiary 84: He was giving his companion a gam, and trying to learn if there was going to be a break.

2. (US) to steal.

1881

Trumble Sl. Dict. (1890).

3. (US black) to boast, to show off.

1944		Cab Calloway New Hepsters Dict. in Calloway (1976) 255: gammin’ (adj.): showing off, flirtatious.
1944		‘Jiver’s Bible’ in D. Burley Orig. Hbk of Harlem Jive.
1972		D. Dalby ‘African element in American English’ in Kochman Rappin’ and Stylin’ Out 180: gam—‘to boast, show off’.