double U

Noun

 * 1) something in the shape of two U's (not of a W)
 * 2) * 1942, Playing Tricks with Plants, Popular Science, Vol. 140, No. 3 (March), p. 110:
 * In training a tree in the double U only the two topmost buds are allowed to grow on the trunk and two arms.
 * In training a tree in the double U only the two topmost buds are allowed to grow on the trunk and two arms.