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 obsolete Russian генварь (genvarʹ, “January”), from Old Church Slavonic генуарь (genuarĭ), генуарии (genuarii), from Ancient Greek Γενάρης (Genárēs), Ἰανουάριος (Ianouários), from Latin Iānuārius, from Iānus (“god in Rome mythology”).
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.