The Collaborative International Dictionary of English v.0.48:

NNW \NNW\ n. (All capitals)
   north northwest; the compass point that is midway between
   north and northwest.

   Syn: north northwest, nor'-nor'-west.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

NNW
    n 1: the compass point that is midway between north and
         northwest [syn: north northwest, nor'-nor'-west, NNW]