The Roman god Janus, associated with doorways and beginnings, gave January its name.
January comes from the Latin name Ianuarius, meaning the month of Janus. Janus was traditionally depicted with two faces, one looking forward and one looking backward. That image made the god a natural symbol for a month associated with leaving the old year and entering the new one.
The Roman calendar was reformed several times, and January did not always occupy exactly the same role in ancient calendrical practice. Under the Julian calendar, January 1 became established as the beginning of the civil year in the Roman world, helping shape the New Year's date used by many later societies.
Janus is not the god of the year itself, and January's name is not derived from the word “January” independently of Latin. The month’s name reflects the Roman religious association with transitions, entrances, and beginnings.