Green’s Dictionary of Slang

(Aus./NZ) a piastre.

1915		Geelong Advertiser (Vic.) 31 July 8/3: Leaving camp at 11 a.m. we proceeded to the tram, had a ‘clean boot, sah,’ for half a ‘disaster’ (piastre), and reached Cairo in time for lunch, which we had at the Petrograd restaurant, a very decent place, where we had a boshta lunch for twelve ‘disasters.’.
1938		Press (Canterbury) 2 Apr. 18: [F]rom Egyptian, ‘buckshee’ and ‘disaster’ for piastre.