Why is the ninth month called September?
mid-14c., "given to worldly activity" (opposed to contemplative or monastic), from Old French actif (12c.) or directly from Latin activus, from actus (see act (n.)). As "capable of acting" (opposed to passive), from late 14c. Meaning "energetic, lively" is from 1590s; that of "working, effective, in operation" is from 1640s. Active voice is recorded from 1765 (grammatical use of active dates from mid-15c.).