Green’s Dictionary of Slang

(UK Und.) a trickster, a fraudster.

1776		Foote Capuchin in Minor Theatre (1794) Act II: After that you turned swindler, and got out of gaol by an act for the relief of insolvent debtors.
1781		G. Parker View of Society II 28: Swindlers [...] was introduced into use in this Country about the end of the last German War [i.e. c.1762]. It was first a cant term. [...] It has since had a legislative adoption, being parliamentarily recognized [...] and swindle, therein, is made to signify the same thing in Law-language which it did in Cant of Flash dialogue.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Swindler, One who obtains goods on credit by false pretences, and sells them for ready money at any price, in order to make up a purse. This name is derived from the German word schwindlin, to totter, to be ready to fall; these arts being generally practised by persons on the totter, or just ready to break. The term swindler has since been used to signify cheats of every kind.
1797		[title] Adventures of the Extravagant Wit; or the English Swindler, shewing the various Frauds and Tricks he committed in London and the most distant parts of the Globe.
1809		G. Andrewes Dict. Sl. and Cant n.p.: Swindlers a set of people who make it a practice to cheat honest tradesmen, under false pretences.
1811		Lex. Balatronicum [as cit. 1785].
1818		W. Perry London Guide 209: swindlers. Their arts and boldness assume so many Protean features, that we despair of giving [...] any thing like so complete an idea of their practices as we have.
1821		‘An Amateur’ Real Life in London I 314: Swindler—Is a term originally derived from the German, Schwindel, which signifies merely to cheat. It was first introduced as a cant term, and used to signify obtaining of goods, credit, or money, under false pretences. It has since had a legislative adoption, being parliamentarily recognised by an Act for the prevention of it.
1836		Marryat Mr Midshipman Easy II 161: ‘Perhaps, sir,’ replied Jack, [...] ‘you will permit us to pay our bill before we go on board. We are no swindlers.’.
1848		Macaulay Hist. of England I Ch. 2 🌐 Bedloe, a noted swindler, followed.
1859		(ref. to 1762) Hotten Dict. of Modern Sl. etc. 106: swindler although a recognised word in respectable dictionaries, commenced service as a slang term. It was used as such by the poor Londoners against the German Jews who set up in London about the year 1762, also by our soldiers in the German War about that time. schwindel, in German, signifies to cheat.