Word Origin & History
c.1300, "to trick, beguile," perhaps from O.Fr. japer "to howl," of echoic origin, or from O.Fr. gaber "to mock, deride." Phonetics suits the former, but sense the latter explanation. Took on a slang sense mid-15c. of "have sex with," and disappeared from polite usage. Revived in harmless M.E. sense
of "say or do something in jest" by Scott, etc.