Why is the ninth month called September?
early 15c., "of or belonging to animals," from Middle French brut "coarse, brutal, raw, crude," from Latin brutus "heavy, dull, stupid," an Oscan word, from PIE root *gwere- "heavy" (see grave (adj.)). Before reaching English the meaning expanded to "of the lower animals." Used of human beings from 1530s.
1610s, from brute (adj.).