Entry 1 sense Webster, 1913 Antagonism /(ăn*tăg"ō̇*nĭz'm)/ · An·tag·o·nism · IPA /ænˈtæɡənɪzəm/ 01 n. Opposition of action; counteraction or contrariety of things or principles. 1. Opposition of action; counteraction or contrariety of things or principles.