Where "Cossie" Comes From
"Cossie" is a clipped and -ie-suffixed form of "costume" — specifically the swimming costume, itself descended from the Victorian-era "bathing costume" that British settlers brought to Australia. As different Australian states developed their own shorthand for swimwear, New South Wales kept the "costume" half and added the diminutive suffix to get "cossie," while Victoria went with "bathers" from the "bathing" half of the compound. The result is a living dialectal divide that still runs along state lines.
The Macquarie Dictionary's Australian Word Map project confirms that "cossie" is most strongly associated with New South Wales and the ACT, while Queensland favours "togs," Victoria favours "bathers," and "swimmers" appears more neutrally across all regions. "Cossie" also appears in South African and some British English, though in Australia it is specifically the NSW marker. The word is informal without being slangy — it appears in news, advertising, and everyday conversation with equal ease. The earliest print citation is from 1926, in J. Doone's book "Timely Tips For New Australians."
Source:
"Grab your cossie, we're heading to the pool."
How Aussies Actually Use It
It's used for swimwear generally, especially in New South Wales, where "cossie" is the dominant term.
Which word Australians use - cossie, bathers, or togs - is a well-known regional giveaway.
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