What is the X in X-mas?
fem. proper name (c.1300), from Old French Margaret (French Marguerite), from Late Latin Margarita, female name, literally "pearl," from Greek margarites (lithos) "pearl," of unknown origin, "probably adopted from some Oriental language" [OED]; cf. Sanskrit manjari "cluster of flowers," also said by Indian linguists to mean "pearl," cognate with manju "beautiful." Arabic marjan probably is from Greek, via Syraic marganitha. The word was widely perverted in Germanic languages by folk-etymology, cf. Old English meregrot, which has been altered to mean literally "sea-pebble."