Green’s Dictionary of Slang

jockum n.

also jockam
[ety. unknown]

[mid-16C–1900s] the penis.

In compounds

jockum cloy (v.) (also jockum) [fig. use of cloy v.]

[late 17C–early 19C] of a man, to have sexual intercourse.

jockum gage (n.) (also jacum-gag) [gage n.1 (2)]

[late 17C–early 19C] (UK Und.) a chamberpot; thus rum jockum gage, a silver chamberpot.

jockum-gagger (n.) (also jack-gagger, jock-gagger) [jock n.1 (1)/ jockum n. + gagger n.1 (3), lit. ‘penis-beggar’]

[late 18C–early 19C] a man who lives on his wife’s prostitution, a pimp.