Why is the ninth month called September?
early 15c., from Middle French permanent (14c.) or directly from Latin permanentem (nominative permanens) "remaining," present participle of permanere "endure, hold out, continue, stay to the end," from per- "through" (see per) + manere "stay" (see mansion). As a noun meaning "permanent wave," by 1909. Of clothing, permanent press attested from 1964.