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

Moby Thesaurus II by Grady Ward, 1.0:

89 Moby Thesaurus words for "southwest":
   Dixie, Dixieland, Down East, East, East Coast, Middle Atlantic,
   Middle West, New England, North, North Central region, Northeast,
   Northwest, Pacific Northwest, SSW, SW, SW by S, South, Southeast,
   Southwest, Sunbelt, West, West Coast, Yankeeland, antarctic,
   arctic, austral, boreal, cardinal points, compass card,
   compass rose, degrees, east, eastbound, easterly, eastermost,
   eastern, easternmost, eastland, eastward, half points, hyperborean,
   lubber line, meridional, north, northbound, northeast,
   northeasterly, northeastern, northerly, northern, northernmost,
   northland, northward, northwest, northwesterly, northwestern,
   occident, occidental, orient, oriental, quarter points, rhumb,
   south, south-southwest, southbound, southeast, southeasterly,
   southeastern, southerly, southern, southernmost, southward,
   southwest by south, southwesterly, southwestern, southwestward,
   southwestwardly, southwestwards, sunrise, sunset, the Coast, west,
   westbound, westerly, western, westernmost, westland, westward,
   wild West