Know how to use "fewer" and "less"? Find out.
late 14c., from Old French ignorant (14c.), from Latin ignorantia, from ignorantem (nominative ignorans), present participle of ignorare "not to know, to be unacquainted; mistake, misunderstand; take no notice of, pay no attention to," from assimilated form of in- "not, opposite of" (see in- (1)) + Old Latin gnarus "aware, acquainted with" (cf. Classical Latin noscere "to know," notus "known"), from Proto-Latin suffixed form *gno-ro-, related to gnoscere "to know" (see know).
Form influenced by Latin ignotus "unknown." Cf. also uncouth. Colloquial sense of "ill-mannered" first attested 1886. As a noun meaning "ignorant person" from mid-15c.