Green’s Dictionary of Slang

1. a loudmouth, a chatterer; a persuasive talker.

1865		Leaves from Diary of Celebrated Burglar 38/1: The reason why Ikey was kept in the dark on this matter was, he was such a rank ‘lushington’ and ‘gaser’ we dared not confide any secret to him.
1879		London Life 24 May 4/2: Little Tom Coyne, the clever Irish "low corr.," met a " gasser " lately, and after some brag on the part of the latter, Tom bought a gold Albert of him for £7 10s.
1905		Truth (Perth) 4 Mar. 2/6: Them Parliamentary gassers / Collars all his bloomin’ stuff.
1912		R.W. Brown ‘Word-List From Western Indiana’ in DN III:viii 576: gasser, n. A talker, especially a braggart. ‘That fellow is the greatest gasser in town.’.
1954		Hepster’s Dict. 4: Gasser – Someone a bit on the obnoxious side, odd ball.
1959		E. De Roo Young Wolves 110: I got no date with him. He’s a gasser.

2. (US black) advice.

1944

D. Burley N.Y. Amsterdam News 29 Jan. 10A: [He] put down a gasser about me copping a pearl diver.