January

January comes from Latin Iānuārius, meaning "(month) of Janus," formed from Iānus plus the adjectival suffix -ārius. The first element may trace back to a Proto-Indo-European root meaning "to go."

The word passed into English through Anglo-Norman genever and Middle English Janevere, before being re-latinised into the Januarie form that gave us modern January.

January is a doublet of Gennaro, both descending from the same Latin root Iānuārius through different paths.