The
Oxford English Dictionary traces singular
they back to 1375, where it appears in the medieval romance
William and the Werewolf. Except for the old-style language of that poem, its use of singular
they to refer to an unnamed person seems very modern. Here’s the Middle English version: ‘Hastely hiȝed
eche . . . þei neyȝþed so neiȝh . . . þere william & his worþi lef were liand i-fere.’ In modern English, that’s: ‘
Each man hurried . . . till
they drew near . . . where William and his darling were lying together.’