Identity comes into English via Middle French identité, ydemtité, ydemptité “the quality of being the same, sameness,” from Late Latin identitās (inflectional stem identitāt- ) “the quality of being the same, the condition or fact that an entity is itself and not another thing.” Identitās is formed partly from the Latin adverb identidem “again and again, repeatedly,” a contraction of idem et idem (“the same and the same”), and partly from Late Latin essentitās, a translation of Greek taủtótēs “identity” (that is, tò auto “the same” and the noun suffix -tēs “-ness”).
“One’s personal characteristics, or the sense of who one is, as perceived by the person or by others,” is a meaning of identity that dates from the early 18th century. Since then, issues of personal identity, especially sexual and gender identity, have provoked discussions about one’s overlapping roles in society. The phrase identity politics “political activity based on or catering to the cultural, ethnic, gender, racial, religious, or social interests that characterize a group identity” was coined in 1973.

Did you mean adenitis?