Words related to idem
c. 1600, "sameness, oneness, state of being the same," from French identité (14c.), from Medieval Latin identitatem (nominative identitas) "sameness," ultimately from Latin idem (neuter) "the same" (see 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 politics is attested by 1987.
"[I]dentity politics" [is] a phrase with notably wide currency in gay and lesbian communities. In common usage, the term identity politics refers to the tendency to base one's politics on a sense of personal identity—as gay, as Jewish, as Black, as female ..... [Diana Fuss, "Essentially Speaking," 1989]