Entry 3 senses · 2 variants Webster, 1913 isolationist /(ī`sō̇*lā"shŭn*ĭst)/ · i·so·la·tion·ist · IPA /ˌaɪsəlˈeɪʃənəst/ n. adj. 01 n. A proponent or supporter of isolationism; one who is isolationistic. 1. A proponent or supporter of isolationism; one who is isolationistic. 02 adj. of or pertaining to isolationism. 1. of or pertaining to isolationism. 2. Favoring or supporting isolationism; -- of people. Syn. isolationist.