Walpurgis night

1820, from German Walpurgisnacht, witches' revel, especially on the Brocken in the Harz Mountains, on May-day eve, literally "the night of (St.) Walpurgis," from Walburga, English abbess who migrated to Heidenheim, Germany, and died there c.780; May 1 being the day of the removal of her bones from Heidenheim to Eichstädt.