Green’s Dictionary of Slang

(orig. Aus.) a bathing costume.

1908		Sun. Times (Perth) 22 Mar. 4/7: Michael’s bathers started early, and they left off quite as soon / They were somewhat wanting at the waist.
1922		Argus (Melbourne) 13 Dec. 6/7: [advert] Holiday Knit Wear Bathers, Ladies’ and Children’s.
1941		Baker Popular Dict. Aus. Sl.
1958		R.M. Stuart in Chamberlain Stuart Affair (1973) 10: She had a white coat on and red bathers.
1970		D. Butts Down Under Up Close 62: They flock to the beaches in brief swimming suits (‘bathing costumes’ or ‘bathers’).
1982		N. Keesing Lily on the Dustbin 105: Once when Australians went to the beach for a ‘dip’ they carried ‘cossies’, ‘bathers’ or ‘togs’ or in South Australia ‘swimmies’.
1992		K. Lette Llama Parlour 104: They want to take pictures of you in your favourite pair of bathers.
1999		G. Seal Lingo 25: The numerous terms for the ‘shorts’ worn when swimming, known variously as bathers (Western Australia), swimmers (New South Wales), cossies or costumes (New South Wales and Victoria), togs (Queensland) and speedos or trunks in different parts of the country.
2003		McGill Reed Dict. of N.Z. Sl.
2007		Orange Coast Mag. May 96/2: A swimsuit (also swimmers), bathing suit (also bathers) [...] or swimming costume.
2020		G. Disher Consolation 3: ‘Not to mention my bathers and best bra.’ ‘Bathers?’ said Hirsch. [...] ‘Water aerobics. Redruth pool’ .