Why is the ninth month called September?
c.1600, "sameness, oneness," from Middle French identité (14c.), from Late Latin (5c.) identitatem (nominative identitas) "sameness," from ident-, comb. form of Latin idem (neuter) "the same" (see identical); abstracted from identidem "over and over," from phrase idem et idem. [For discussion of Latin formation, see entry in OED.] Earlier form of the word in English was idemptitie (1560s), from Medieval Latin idemptitas. Term identity crisis first recorded 1954. Identity theft attested from 1995.
identity i·den·ti·ty (ī-děn'tĭ-tē)
The set of behavioral or personal characteristics by which an individual is recognizable as a member of a group.
The distinct personality of an individual regarded as a persisting entity; individuality.