What is the X in X-mas?
late 13c. (mid-12c. as a surname), from Anglo-French fesaunt, Old French faisan (13c.) "pheasant," from Latin phasianus, from Greek phasianos "a pheasant," literally "Phasian bird," from Phasis, river flowing into the Black Sea in Colchis, where the birds were said to have been numerous. The ph- was restored in English late 14c. (see ph). The excrescent -t is due to confusion with -ant suffix of nouns formed from present participle of verbs in first Latin conjugation (peasant, tyrant, etc.).