Green’s Dictionary of Slang

1. to lie down, to sleep.

c.1566		Harman Caveat for Common Cursetours in Viles & Furnivall (1907) 84: In what lipken has thou lypped in this darkemans, whether in a lybbege or in the strummell?
1608		Dekker Belman of London (3rd) B4: [as cit. c.1566].
1611		Middleton & Dekker Roaring Girle V i: O I wud lib all the lightmans. / O I woud lib all the darkmans.
1688		R. Holme Academy of Armory Ch. iii item 68c: Canting Terms used by Beggars, Vagabonds, Cheaters, Cripples and Bedlams. [...] Lib, ly, lye down.

2. to sleep together, to have sexual intercourse.

1637		Dekker ‘Canting Song’ in Eng. Villainies (8th edn) O2: Store of Stroommell weele have here, and i’th skipper Lib in state.
a.1674		‘The Rogues . . . praise of his Stroling Mort’ Head Canting Academy (1674) 19: [as cit. 1637].
c.1698		B.E. Dict. Canting Crew n.p.: Lib, to Tumble or Lye together.
1707		‘Maunder’s Praise of His Strowling Mort’ in Farmer Musa Pedestris (1896) 33: [as cit. 1637].
1725		New Canting Dict. [as cit. c.1698].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
1754		Scoundrel’s Dict. 19: To tumble together – Lib.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1809		G. Andrewes Dict. Sl. and Cant n.p.: libb to lie together, mess together.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1835		G. Kent Modern Flash Dict. 20: Lib – to live together.
1848		Flash Dict. in Sinks of London Laid Open [as cit. 1835].