Green’s Dictionary of Slang

eight shillings (40p).

1859		Hotten Dict. of Modern Sl. etc. 130: THEG, or teaich gens, eight shillings.
1864, 1867, 1870		Hotten Sl. Dict. [as cit. 1859].
1873		Sl. Dict.
1890–1904		Farmer & Henley Sl. and Its Analogues.
2011		Spitalfields Life 18 Nov. 🌐 ‘Thgiet’ is ‘eight’ backwards.