winglet

Short definition from Wiktionary

Noun

1. 1
   A little wing.
2. 2
   A winglike structure at a wingtip set at an angle to the plane of the wing designed to reduce drag by its effect on wingtip vortices.
3. 3
   The bastard wing or alula of a bird.
4. 4
   The pterygium of a weevil.