Entry 1 sense Webster, 1913 Southwestern /southˌ-wĕs'-tẽrn/ · South·west·ern · IPA /sˌaʊθwˈɛstərn/ 01 a. Of or pertaining to the southwest; southwesterly; as, to sail a southwestern course. 1. Of or pertaining to the southwest; southwesterly; as, to sail a southwestern course.