Green’s Dictionary of Slang

(Aus.) a communist, or one whose views, from hard left to mildly liberal, are seen as deviant from the speaker’s (right-wing/conservative) ‘norm’; also as adj.

1934		Williamstown Chron. (Vic.) 3 Nov. 6/4: One lady in particular at that meet ing put the ‘commo’ stuff over. The Communist is one branch of political thought that I am howling crook on.
1938		Workers’ Wkly (Sydney) 22 Nov. 2/4: ‘And how are the “Commos” doing over there,’ we butted in. ‘Well there are 400 members and indications are for a rapid increase in membership’.
1941		Baker Popular Dict. Aus. Sl.
1945		Worker (Brisbane) 19 Mar. 2/5: [headline] ‘Commo Tactics’.
1949		D. Walker We Went to Aus. 193: A communist is a ‘Commo’.
1951		(con. 1941) E. Lambert Twenty Thousand Thieves 175: Fancies himself, the bloody Commo.
1955		J. Morrison Black Cargo 216: More bloody commo politics!
1965		L. Haylen Big Red 187: ‘Commo crap,’ said Timmy.
1965		W. Dick Bunch of Ratbags 206: The Commos would call the boss a capitalist if he was in Russia.
1976		D. Ireland Glass Canoe (1982) 69: ‘I think you’re all commos,’ Ernie said. Me, I think there’s three estates: communists, capitalists and the poor, with the third estate the most numerous.
1986		R. Fitzgerald Pushed from the Wings (1989) 69: Fairies, lesbos, commos, Trots, radical coons – what’s this bloody state come to?
1993		B. Moore Lex. of Cadet Lang. 88: Thus a commie/commo could well be e.g. a Liberal Party ‘wet’, a hard-nosed member of the Labour Party’s socialist left, or a completely apolitical person.
2001		(con. 1945–6) P. Doyle Devil’s Jump (2008) 48: ‘Bludging power workers [...] Wouldn’t work in an iron lung.’ ‘It‘s the bloody commos,’ he said. [Ibid.] 55: Give them the secret commo handshake or whatever you do.
2012		(con. 1943) G.S. Manson Irish Fandango [ebook] Len was a right commo when it came down to it.
2021		J. Ellroy Widespread Panic 158: Robin Redbreast was a crazy Commo in the ’30s.