The Collaborative International Dictionary of English v.0.48:

Southwest \South`west\ (?; colloq. sou"-.), n.
   The point of the compass equally from the south and the west;
   the southwest part or region.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Southwest \South`west"\, a.
   Pertaining to, or in the direction of, the southwest;
   proceeding toward the southwest; coming from the southwest;
   as, a southwest wind.
   [1913 Webster]

WordNet (r) 3.0 (2006):

southwest
    adv 1: to, toward, or in the southwest [syn: southwest,
           south-west, sou'west]
    adj 1: coming from the southwest; "the winds are southwesterly"
           [syn: southwesterly, southwest]
    2: situated in or oriented toward the southwest [syn:
       southwest, southwestern, southwesterly]
    n 1: the compass point midway between south and west; at 225
         degrees [syn: southwest, sou'-west, southwestward,
         SW]
    2: the southwestern region of the United States generally
       including New Mexico, Arizona, Texas, Nevada, California, and
       sometimes Utah and Colorado [syn: Southwest, southwestern
       United States]
    3: the direction corresponding to the southwestward compass
       point
    4: a location in the southwestern part of a country, region, or
       city