Green’s Dictionary of Slang

1. a 20-shilling piece.

1648		Dekker Canters Dict. in Eng. Villainies (9th edn) n.p.: Harts ease. Twenty shillings.
1665		Head Eng. Rogue I 50: Hearts ease, A twenty shillings piece.
c.1698		B.E. Dict. Canting Crew n.p.: Hearts-ease, a Twenty shilling piece; also an ordinary sort of Strong Water.
1725		New Canting Dict. [as cit. c.1698].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.

2. a measure of gin.

c.1698		see sense 1.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.