January: [14] The ancient Romans had a god named Janus whose head had two faces, looking in opposite directions. He was the tutelary deity of doorways, and his festival month was at the beginning of the year, when he could look both backwards at the old year and forwards to the new one. This month was therefore called Jānuārius mensis ‘month of Janus’ – whence English January. [January etymology, January origin, 英语词源]