Why is the ninth month called September?
late 15c., mappe "bundle of yarn, etc., fastened to the end of a stick for cleaning or spreading pitch on a ship's decks," from Walloon (French) mappe "napkin," from Latin mappa "napkin" (see map (n.)). Modern spelling by 1660s. Of hair, from 1847.
1709, from mop (n.). Related: Mopped; mopping.
[1944+ Black; probably from the notion of mopping or cleaning up, influenced by earlier jazz use ''the last beat at the end of a jazz number'']