late 14c., "to trick, beguile, jilt; to mock," also "to act foolishly; to speak jokingly, jest pleasantly," perhaps from Old French japer "to howl, bawl, scream" (Modern French japper), of echoic origin, or from Old French gaber "to mock, deride." Phonetics suits the former, but sense the latter explanation. Chaucer has it in the full range of senses. Around mid-15c. the Middle English word took on a slang sense of "have sex with" and subsequently vanished from polite usage. It was revived in the benign sense of "say or do something in jest" by Scott, etc., and has limped along since in stilted prose. Related: Japed; japing.
mid-14c., "a trick, a cheat;" late 14c. "a joke, a jest; a frivolous pastime, something of little importance" (late 14c.); see jape (v.). By 1400 also "depraved or immoral act; undignified behavior; bawdiness." Related: Japery "jesting, joking, raillery, mockery" (mid-14c.).