Why is the ninth month called September?
late 14c., "quick stroke, sweeping movement," probably from Old Norse visk "wisp," from Proto-Germanic *wisk- "move quickly" (cf. Middle Dutch wisch, Dutch wis, Old High German wisc, German wisch "wisp, brush"), from PIE root *weis- "to turn, twist" (cf. Sanskrit veskah "noose," Czech vechet "a wisp of straw"). Meaning "implement for beating eggs, etc." first recorded 1570s.
late 15c., from a Scandinavian source (cf. Danish viske, Norwegian, Swedish viska) related to Old English wiscian "to plait," weoxian "to clean" (with a whisk or brush), granwisc "awn" (see whisk (n.)). Related: Whisked; whisking.