Green’s Dictionary of Slang

a groat, fourpence.

c.1698		B.E. Dict. Canting Crew n.p.: Crokers c. a Groat or Four-pence. The Cull tipt me a Croker, c. the Fellow gave me a Groat.
1725		New Canting Dict. [as cit. c.1698].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
c.1750–1882		B.M. Carew Life and Adventures.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1809		G. Andrewes Dict. Sl. and Cant.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
c.1850		Duncombe New and Improved Flash Dict. n.p.: Croaker a groat.