Green’s Dictionary of Slang

earnest n.

[SE earnest, money, esp. as paid as a pledge for securing a contract]

(UK Und.) a share (of the booty); thus tip someone their earnest, to hand out a share.

[UK]Dekker Canters Dict. Eng. Villainies (9th edn) n.p.: Earnest a part, Tip me my Earnest, give me my share.
[UK]Head Eng. Rogue I 49: [as cit. 1648].
[UK]Head Canting Academy (2nd edn).
[UK]B.E. Dict. Canting Crew n.p.: Earnest c. Part or Share. Tip me my earnest, c. give me my Snack or Dividend.
[UK]A. Smith Lives of Most Noted Highway-men, etc. I 209: Tip me my Earnest, that’s give me my Part or Share.
[UK]Defoe Street Robberies Considered 31: Earnest, Share.
[UK]Bailey Universal Etym. Eng. Dict. [as cit. c.1698].