Origin uncertain. 1. It is said to be a Huguenot name, probably a derivative of French Isle D’Aix, a habitational name from a place in Charente Maritime, or Dildé, which is of uncertain origin. 2. Alternatively, perhaps, a respelling of German Dildey, which is likewise unexplained. The element -dey, which occurs in a number of German surnames (e.g. Dauthendey, Mackeldey), has so far received no satisfactory explanation.