Green’s Dictionary of Slang

a shilling.

1857		‘Ducange Anglicus’ Vulgar Tongue.
1863		Story of a Lancashire Thief 9: There was Downy, a Turkey merchant in a small way, who had such a feeling for tusheroons that he was always changing his tanners and stags, and aldermen, into them.
1873		Sl. Dict.
1881		Morn. Bulletin (Rockhampton, Qld) 18 July 2/6: For a shilling there are many names but nearly all slang. [...] ‘Breaky-leg,’ ‘brongs,’ ‘bobs,’ ‘bordes,’ ‘drawers,’ ‘gens’, ‘hogs,’ levys,’ ‘pegs,’ ‘stags,’ ‘Shigs,’ ‘twelvers’ and ‘teviss’s’ .
1887		W.E. Henley ‘Villon’s Straight Tip’ in Farmer Musa Pedestris (1896) 177: You cannot bank a single stag: / Booze and the blowens cop the lot.
1925		(ref. to 1850s) Western Mail (Perth) 28 May 21/1: [from Daily Mail, London]At the time of the Crimean War bob was only one of a number of terms [for a shilling] such as twelver and breaky-leg, gen and teviss, stag, deaner, hog and levy.