late 13c., Ieneuer (early 12c. in Anglo-French), from Old North French Genever, Old French Jenvier (Modern French Janvier), from Latin Ianuarius (mensis) "(the month) of Janus" (q.v.), to whom the month was sacred as the beginning of the year according to later Roman reckoning (cognates: Italian Gennaio, Provençal Genovier, Spanish Enero, Portuguese Janeiro). The form was gradually Latinized by c. 1400. Replaced Old English geola se æfterra "Later Yule." In Chaucer, a type-name for an old man.