I learnt an interesting new French word today – célibataire. When I first saw it I guessed that it meant celibate, but when I checked in a dictionary I found that while it does mean celibate, it is more commonly used to mean single. So un célibataire is a single man or bachelor, and une célibataire is a single woman or spinster. A confirmed bachelor un célibataire endurci and une mère célibataire is a single / unmarried mother – the male equivalent is un père célibataire.
Célibataire comes from célibat (celibacy), from the Latin caelebs (unmarried, single), from the Proto-Indo-European *kaiwelo- (alone) and *libʰs– (living) [source].
Single comes from the Middle English sengle, from the Old French sengle, from Latin singulus, a diminutive of simplex (simple or literally “onefold”*, from sim- (the same) and plicare (to fold) [source].
*Duplex = twofold, double
Also occasionally “célibatrice ” for the female version can be heard. It’s officially incorrect (the French are amazingly certain as to what is correct and not!) but is a sufficiently frequent error in colloquial French for there to be discussion of it on the internet.