Green’s Dictionary of Slang

the all-in-one underwear known as combinations.

c.1910		H. Waddell letter in F. Corrigan H. Waddell 83: Many thanks for the combies—I put lace round the top and ran blue ribbon through it: they were a great comfort to me.
1914		E. Wittmann ‘Clipped Words’ in DN IV:ii 126: combie, i.e. combination. A woman’s under garment.
1920		Hartlepool Mail 27 Mar. 1/4: [advert] Dainty Lingerie [...] Knicks...Combies...Chems...Cams.
1930		J.P. McEvoy Hollywood Girl 223: I busted all my combies laughing.
1942		Sunderland Echo 2 Jan. 3/5: [advert] Cosy Combies, woollen plated Botany finish.
1981		P. White Flaws in the Glass 5: I was kept out of draughts and protected by woollen combies.
1985		(con. 1920s) A. Blair Tea at Miss Cranston’s (1991) 15: And the next-to-skin garb most universally loathed was undoubtedly combinations. Miss Nancy Wall speaks for generations of the tormented, buttoned into combies, ‘I hated them ... all tight and sore between your legs’.