1530s, "ungentlemanly, base, mean," from Middle French illiberal (14c.), from Latin illiberalis "ungenerous, mean, sordid; unworthy of a freeman," from assimilated form of in- "not, opposite of" (see in-(1)) + liberalis (see liberal). A sense of "narrow-minded politically; unconcerned with the rights or liberties of others" is attested from 1640s, and might conceivably be revived to take up some of the burden that drags down conservative.