Merriam-Webster Collegiate Dictionary - southwest

 I. adverb  Date: before 12th century to, toward, or in the ~  II. noun  Date: 12th century  1.  a. the general direction between south and west  b. the point midway between the south and west compass points  2. capitalized regions or countries lying to the ~ of a specified or implied point of orientation  III. adjective  Date: 14th century  1. coming from the ~ a ~ wind  2. situated toward or at the ~ the ~ corner