Green’s Dictionary of Slang

1. a thief who robs travellers staying in taverns or alehouses.

1754

Scoundrel’s Dict. 29: The Jilt is one that pretending Business in a Tavern or Alehouse, takes a private Room, and with Pick-locks opens the Trunks or Chests, and taking what he can conveniently, locks ’em again, pays his Reckoning and departs.

2. a crowbar, housebreaking tools in general.

1859		Hotten Dict. of Modern Sl. etc. 54: JILT, a crowbar.
1864, 1867, 1870		Hotten Sl. Dict. [as cit. 1859].
1869		Australiasian (Melbourne) 17 July 8/5: A crowbar is a jemmy and jilt. The boy who is put in at the window to open the door is called a little snake.