Green’s Dictionary of Slang

gig v.2

[? gig n.12 ]

to have a form of sexual intercourse considered as ‘deviant’, poss. anal intercourse.

[UK]Machine 11: Selfish Letcher that does Jesuit box, / Or Huffling, Gigging, Semigigging, Larking, / Or that queer Practice, by the Cull call’d Barking.