Green’s Dictionary of Slang

cashish n.

[SE cash + hashish (as a desirable/valuable commodity)]

money.

[UK]J.J. Connolly Layer Cake 89: I’ll give you two grand cashish over the top.
[UK]J.J. Connolly Viva La Madness 144: In the safe they found [...] bundles of cashish — pounds, euros and dollars.