Green’s Dictionary of Slang

lig n.1

[? dial. lig, to lie down or lib-beg n.]

a bed.

[UK]Grose Classical Dict. of the Vulgar Tongue.
[UK]Lex. Balatronicum.
[UK]Egan Grose’s Classical Dict. of the Vulgar Tongue.
[US]Matsell Vocabulum 51: lig A bedstead.

In compounds

lig robber (n.)

a thief who hides under a bed waiting to rob or assault somebody.

[US]Irwin Amer. Tramp and Und. Sl. 121: Lig Robber. – A thief who hides under a bed or in a closet until the woman is alone in the house, when she is robbed and possibly assaulted.
[US]Monteleone Criminal Sl. (rev. edn) 145: lig robber One who hides in a bed room waiting to rob or assault the victim.