Yours, Etc.: Origins and Uses of 8 Sign-Offs
late 14c., "taking words in their natural meaning" (originally in reference to Scripture and opposed to mystical or allegorical), from Old French literal and directly from Late Latin literalis/litteralis "of or belonging to letters or writing," from Latin litera/littera "letter, alphabetic sign; literature, books" (see letter (n.1)). Meaning "of or pertaining to alphabetic letters" is from late 15c. Sense of "verbally exact" is attested from 1590s, as is application to the primary sense of a word or passage. Literal-minded is attested from 1791.