Why is the ninth month called September?
Old English niþera, neoþera "down, downwards, below, beneath," from Proto-Germanic *nitheraz (cf. Old Saxon nithar, Old Norse niðr, Old Frisian nither, Dutch neder, German nieder), from comparative of PIE *ni- "down, below" (cf. Sanskrit ni "down," nitaram "downward," Greek neiothen "from below," Old Church Slavonic nizu "low, down"). Has been replaced in most senses by lower (adj.).