Green’s Dictionary of Slang

1. (US) to cheat, to delude, to humbug.

1840		Spirit of the Times (N.Y.) 5 Sept. 324/3: You are attempting to gum us with these pretended expenses [DA].
1848		J.R. Lowell Biglow Papers (1880) 118: You can’t gum me, I tell ye now.
1859		G.A. Sala Twice Round the Clock 218: I began to think either that he was quizzing me – ‘gumming’ is the proper Transatlantic colloquialism, I think.
1875		Amer. Eng. in Chamber’s Journal 25 Sept. 611: To ‘gum-tree’ is to elude, to cheat [from opossum], and this again is shortened into ‘to gum,’ as the phrase, ‘Now don’t you try to gum me.’ [F&H].
1882		E.S. Ellis Huge Hunter in Beadles Half Dime Library XI:271 5/1: Jerusalem! they’ll be sure to pay us a visit—I’ll be gummed if they won’t.

2. (US campus) to cheat (in an examination).

1856

B.H. Hall College Words (rev. edn) 244: gum. [...] to cheat in recitation by using ponies, interliners, &c.