early 15c., "uneducated, unable to read (originally of Latin)," from Latin illiteratus "unlearned, unlettered, ignorant; without culture, inelegant," from assimilated form of in- "not, opposite of" (see in-(1)) + literatus, literally "furnished with letters" (see literate). Rendered in Old English as unstæfwis. As a noun meaning "illiterate person" from 1620s. Hence, illiterati (1788).