Green’s Dictionary of Slang

1. (orig. Aus./S.Afr.) a swimming costume.

1926		J. Doone Timely Tips For New Australians 17: COSSIE. — A sea-side term applied to a swimming costume.
1949		Argus (Melbourne) 1 Oct. 11/3: If the same sninny is of elegant proportions and gets into a cossie she looks ribuck, meaning that she is most attractive in a swimming costume.
1956		Aus. Women’s Wkly 7 Mar. 29: [heading] They’ve glamorised the old cotton cossie.
1959		D. Hewett Bobbin Up (1961) 57: The cozzies and towel [were] rolled under Ken’s arm.
1981		C. Hope Separate Development 16: It was the cozzie designed for a stripling pressed into the service of a well-endowed Harry Moto.
1982		N. Keesing Lily on the Dustbin 88: Backless dresses and swimming ‘cossies’ with halter necks were frowned upon.
1986		F. Taylor Auf Wiedersehen Pet Two 198: And show up to work in a cossy, that’s the idea.
1986		R.G. Barrett Godson 13: ‘I knew I should have brought my cossies’.
1992		K. Lette Llama Parlour 23: I squirmed back into my cossie.
1993		Aus. Word Map 🌐 cozzie [...] alternative spelling for cossie.
1999		Guardian Weekend 14 Aug. 29: Over your chosen cozzie, put a sleeveless [...] top.
2003		McGill Reed Dict. of N.Z. Sl.
2008		Cape Argus (S. Afr.) 28 Jan. 8: Borat cozzie banned at NZ ‘family event’.
2024		J. Meades Empty Wigs (t/s) 712: ‘I haven’t got a cozzie.’ ‘Neither have I... Don’t worry - there’s never anyone around’.

2. (Aus./UK) any form of costume, e.g. fancy dress, a suit.

1974–5		B. Humphries Barry McKenzie [comic strip] in Complete Barry McKenzie (1988) 119: I’m gunna stick out like a sore toe unless old Rose shows up with a spare cozzie.
1996		Penguin Bk of More Aus. Jokes 358: ‘Is this your first time in Sydney?’ the taxidriver inquired of a Scotsman wearing the full cossie of kilt and sporran. [Ibid.] 432: The ball was a great success and Dave and Mabel won the prize for the most original cossie.
2019		P. Baker Fabulosa 290/2: cossy costume.
2023		R. Milward Man-Eating Typewriter 41: After experimenting for months on the sewing-vacaya, she conjured up a strange range of cozzies for me.