Why is the ninth month called September?
1540s, from Latin perpetratus, past participle of perpetrare "to perform, to accomplish," from per- "completely" + patrare "carry out," originally "bring into existence," from pater "father" (see father (n.)). Earlier in English was perpetren, mid-15c., from Old French perpetrer. Neither good nor bad in Latin, first used in English in statutes, hence its sense of "to perform criminally." Related: Perpetrated; perpetrating.