Green’s Dictionary of Slang

1. easy, comfortable, undemanding.

1894		Civil & Milit. Gaz. (Lahore) 18 Oct. 4/3: So ’oping my letter’ll find yer / A.1. an’ all cush.
1901		Bulletin (Sydney) 14 Dec. Red Page/3: Among other slang phrases are the words ‘screw’ for salary or income, ‘narked’ for angry, ‘cush’ for comfortable, and ‘putting on side’ for putting on airs.
1914		Truth (Melbourne) 31 Jan. 6/1: Boskerino! Cush, and all sigarnio, my oath!
1932		(con. 1917–19) Dos Passos Nineteen Nineteen in USA (1966) 605: He got this cush job in the Post Despatch Service.
1945		Baker Aus. Lang.
1983		C. Heath A-Team 2 (1984) 134: I could break out of this cush joint on horseback with a bad case of flu.

2. (Aus.) fair, honourable [? another ety. might apply].

1897		W.T. Goodge ‘Great Aus. Slanguage’ in Baker Aus. Lang. (1945) 117: But when things go as he wants ’em / He declares it is all cush.
1900–10		Stephens & O’Brien Materials for a Dict. of Aus. Sl. [unpub. ms.] 54: CUSH – fair, square, from Hebrew kosher – lawful.
1901		Sydney Sportsman (Surry Hills, NSW) 25 Sept. 3/2: You should see me in my Sunday / ‘Clobber’ / [...] / In company with Florrie, looking ‘koosh’.
1955		N. Pulliam I Travelled a Lonely Land (1957) 232/1: cush – fair (adj.).