köken: Attested since 1171. From Old Spanish janero, jenero, from Vulgar Latin ienuārius, from Classical Latin Iānuārius (“(month) of Janus”), from Iānus (“Roman god of doorways”), from iānua (“passage”), from Proto-Indo-European *h₁ey- (“to go”) or Proto-Indo-European *yeh₂-; cf. Sanskrit यान (yāna). Cognates with English January, Italian gennaio, French janvier and Portuguese janeiro to name few, see…
köken: From Old Swedish thorsmanadher, equivalent to Tor (“Thor”) + -s- + månad (“month”). First attested in the early half of the 15th century. Probably related to Old Norse þorri.
köken: Etymology tree Proto-Indo-European *yeh₂-der. Latin iānus Latin Iānus Proto-Indo-European *-yósder. Proto-Italic *-āzijos Latin -ārius Latin Iānuāriusder. Anglo-Norman geneverbor. Middle English Janevere Middle English Januarie English Januarybor. Classical Persian جَنْوَرِی (janwarī)bor.? Hindi जनवरी Borrowed from English January. Possibly through Classical Persian جَنْوَرِی (janwarī).
köken: tammi (“heart, core, axis”) (archaic) + kuu (“month”); January marks the center of the winter. Alternatively from tammi (“oak (tree)”) (because oak wood is rather hard, evoking the 'hard', i.e. harsh, cold weather).
aile: tammikuinen
Tammikuun ensimmäinen päivä on myös vuoden ensimmäinen päivä.