Green’s Dictionary of Slang

1. (UK Und.) a half guinea or ten shillings (50p).

1688		T. Shadwell Squire of Alsatia I i: Megs are guineas, smelts are half-guineas.
c.1698		B.E. Dict. Canting Crew n.p.: Smelts c. half Guineas. Tip me a Smelt, c. Prithee lend me half a Guinea.
1709		N. Ward Compleat and Humorous Account of Remarkable Clubs (1756) 228: Then on with your Night-Caps and tie up your Legs, / A Begging let’s go for the Smelts and the Megs.
1725		New Canting Dict. [as cit. c.1698].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. n.p.: smelts Half-Guineas.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
a.1790		H.T. Potter New Dict. Cant (1795).
1809		G. Andrewes Dict. Sl. and Cant.
1811		Lex. Balatronicum.
1812		Spirit of Irish Wit 261: If I have a hog, / A smelt, a George, or a tester.
1822		(con. early 17C) Sir W. Scott Fortunes of Nigel II 282: That noble Master Grahame, whom you call Green, has got the decuses and the smelts.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1835		G. Kent Modern Flash Dict.
1848		Flash Dict. in Sinks of London Laid Open.
1905		Exeter & Plymouth Gaz. 4 Feb. 5/6: Ten shillings is known in some circles as a ‘half-bean’ and a ‘smelt’.
1919		Smith’s Wkly (Sydney) 7 June 9/6: Slang of Money [...] 10/- is a ‘half bean,’ a ‘smelt’.

2. (US) a five-dollar piece, a ‘half-eagle’.

1859		Matsell Vocabulum.
1860		N.E. Police Gaz. (Boston, MA) 18 Aug. 8/2: How about that ‘lone widder’ you visit so much [...] do you give her smelts?
1882		Dly Dispatch (Richmond, VA) 1 Nov. 3/3: ‘Smelts’ means a $5 gold piece.