Entry 1 sense Webster, 1913 Outermost /out'-ẽrm-ōstˌ/ · Out·er·most · IPA /ˈaʊtɚmoʊst/ 01 a. Being on the extreme external part; farthest outward; as, the outermost row. 1. Being on the extreme external part; farthest outward; as, the outermost row.