Green’s Dictionary of Slang

sham adj.

fake, deceitful, cheating.

1741		Ordinary of Newgate Account of the Malefactors executed at Tyburn 18th March 1740 part II 7: The next exploit Jenny went upon was, Slanging the Gentry Mort rumly with a sham Kinchin [...] dressing herself very genteely like a Citizen’s Wife big with Child, with a Pillow artfully fixed under Coats.
1750		Newcastle Courant 28 July 2/1: On Examination of one of them, who stiled himself her Brother, it was soon discovered to be a sham Plea.
1811		Lex. Balatronicum n.p.: The file kidded the joskin with sham books, and his pall capped; the deep one cheated the countryman with false cards, and his confederate assisted in the fraud.
1846		South Australian (Adelaide) 15 May4/3: [from London press] Travelling tinkers make sham gold rings out of old brass buttons.
1882		Manchester Courier 28 Jan. 10/6: All his spare time was taken up writing sham testimonials .
1882		Dundee Courier (Scot.) 1 Sept. 7/3: The other sham sailor has recently been in Hull.

In compounds

shambrucks (n.)

nonsense, a fake.

1757

Smollett Reprisal I ii: Arra, upon my conscience I believe it is simple shambrucks, honey.

In phrases

sham-plot (n.)

a conspiracy.

1722		R. Wodrow Analecta II (1842) 366: Thus gentlemen were first attacked [...] threatened with ruin, and forced to fly the country, and then forfaulted for sham-plots.
1740		R. North Examen 256: It will lay open the Mystery of this Sham-plot.