late 13c., Ieneuer, from Old North French Genever, Old French Jenvier (Modern French Janvier), attested from early 12c. in Anglo-French, from Latin Ianuarius (mensis) "(the month) of Janus," to whom the month was sacred as the beginning of the year (see Janus; cognates: Italian Gennajo, Provençal Genovier, 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.