Green’s Dictionary of Slang

intelligence, native wit.

1920		Chambers’s Journal 13 Mar. 233/1: If they weren’t so sure of getting me, they would have had the gump to wait a few days till the court adjourns .
1941		J.M. Cain Mildred Pierce (1985) 440: They were too lazy to work, and you couldn’t tell her that anybody couldn’t get along [...] if they only had a little gump.
1968		K. Bird Smash a Glass Image 10: A phoney who hasn’t the gump to feed and exercise properly .