Green’s Dictionary of Slang

1. a contraceptive sheath.

1958		A. Sillitoe Sat. Night and Sun. Morning 58: What’s the good o’ going wi’ a married woman if you’ve got to use a frenchie?
1971		(con. WWII) B. Aldiss Soldier Erect 68: I got up [...] pulling the sodden frenchie off my prick.
1975		R. Macklin Queenslander 33: He hadn’t used a frenchy either.
1985		B. Humphries Traveller’s Tool 33: Take a good supply of Frenchies.
1999		G. Seal Lingo 126: In Lingo, condoms are [...] frenchies.
2017		T. Spicer Good Girl Stripped Bare 21: I’m sensible enough not to shag or root any of them – with or without a ‘frenchie’.
2024		J. Meades Empty Wigs (t/s) 717: [A] halfwitted editorial apprentice who seemed to think a frenchie was a toasted sandwich.

2. in pl., French knickers.

2005

Jade LB Keisha the Sket (2021) 76: He slid his hands down ma frenchies n started caressin ma bum.