Why is the ninth month called September?
mid-15c., "a going away, act of leaving," from Old French departement (12c.) "division, sharing out; divorce, parting," from Late Latin departire (see depart). French department meant "group of people" (as well as "departure"), from which English borrowed the sense of "separate division, separate business assigned to someone in a larger organization" (c.1735). Meaning "separate division of a government" is from 1769. As an administrative district in France, from 1792.