The Collaborative International Dictionary of English v.0.48:

Northwestern \North`west"ern\, a.
   Of, pertaining to, or being in, the northwest; in a direction
   toward the northwest; coming from the northwest;
   northwesterly; as, a northwestern course.
   [1913 Webster] Northwestward

WordNet (r) 3.0 (2006):

northwestern
    adj 1: situated in or oriented toward the northwest [syn:
           northwestern, northwesterly, northwest]
    2: of a region of the United States generally including
       Washington; Oregon; Idaho; and sometimes Montana; Wyoming