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