Entry 2 senses · 2 variants Webster, 1913 activist · IPA /ˈæk.tɪ.vɪst/ n. adj. 01 n. one who is aggressively active on behalf of a cause. 1. one who is aggressively active on behalf of a cause. Syn. militant 02 adj. advocating a cause or engaged in activism 1. advocating a cause or engaged in activism