What is the X in X-mas?
late 14c., "riotous merry-making," from Old French revel "entertainment, revelry," verbal noun from reveler "be disorderly, make merry" (see revel (v.)). Related: Revels; revel-rout.
early 14c., "to feast in a noisy manner;" late 14c., "take part in revels," from Old French reveler, also rebeller "be disorderly, make merry; rebel, be riotous," from Latin rebellare "to rebel" (see rebel (v.)). The meaning "take great pleasure in" first recorded 1754. Related: Reveled; reveling; revelled; revelling.