Green’s Dictionary of Slang

gum v.2

also gum up

1. [20C+] (US) to mess up, to spoil.

2. [1930s+] to talk nonsense.

In compounds

gumbrain (n.) (also gumbook, gumhead)

[1950s+] (US) an idiot.

In phrases

gum the game (v.) (also gum the play, ...show)

[1910s–60s] to spoil.

gum (up) the works (v.) (also gum things up, gum up the game, ...inner workings, ...job)

[1910s+] to make a mess, to cause an obstruction.