Why is the ninth month called September?
1690s, "management of a household, domestic establishment," from French ménage, from Old French manage "household, family dwelling" (12c.), from Vulgar Latin *mansionaticum "household, that which pertains to a house," from Latin mansionem "dwelling" (see mansion). Now generally used in suggestive borrowed phrase ménage à trois (1891), literally "household of three." Borrowed earlier as mayngnage, maynage and in the sense "members of a household, a man's household" (c.1300); but this was obsolete by c.1500.