October
late Old English, from Latin, from octo ‘eight’ (being originally the eighth month of the Roman year).
wiktionary
From Middle English, borrowed from Old French octobre, from Latin octōber(“eighth month”), from Latin octō(“eight”), from Proto-Indo-European *oḱtṓw(“twice four”); + Latin -ber, from -bris, an adjectival suffix; October was the eighth month in the Roman calendar.
etymonline
October
late Old English, from Latin October (mensis), from octo "eight," from PIE root *octo(u)- "eight" (see eight). The eighth month of the old Roman calendar (pre-46 B.C.E.), which began the year in March. For -ber see December. Replaced Old English winterfylleð. In Russian history, the October Revolution (in which the Bolsheviks overthrew the Provisional Government) happened Nov. 7, 1917, but because Russia had not at that time adopted the Gregorian calendar reform, this date was reckoned there (Old Style) as Oct. 25.
