Janus, the two-faced Roman god, gave January its name.
Janus was associated with beginnings, transitions, doorways, gates, and passages. His two faces were traditionally understood as looking in opposite directions, often interpreted as looking toward the past and the future. That symbolism connects naturally with the transition marked by New Year’s Eve.
The Latin month name Ianuarius developed from Janus’s name and became January in English. In the Roman calendar tradition, January eventually became the first month of the year, although earlier Roman calendars had used March as the beginning.
Janus is not the source of the name New Year’s Eve itself. The connection is cultural and calendrical: January begins immediately after December 31, while Janus represents thresholds and new beginnings. Janus is also distinct from Saturn, whose festival Saturnalia is often associated with Roman winter celebrations but did not create the name January.