What is the X in X-mas?
"reward, recompense" (now only poetic), late 14c., from Old French guerdon, guerredon "reward, recompense, payment," from Medieval Latin widerdonum, from Old High German widarlon "recompense;" cf. Old English wiðerlean "requital, compensation," from wiðer "again" (see with) + lean "payment." Form influenced in Medieval Latin by Latin donum "gift." Cf. Spanish galardon, Italian guiderone.