unilateralism Syllabification: (u·ni·lat·er·al·ism)Pronunciation: /ˌyo͞onəˈlatərəˌlizəm, -ˈlatrə-/Definition of unilateralism noun the process of acting, reaching a decision, or espousing a principle unilaterally. the pursuit of or belief in unilateral nuclear disarmament:the party’s commitment to unilateralismDerivatives unilateralist noun & adjective unilateralism in other Oxford dictionaries Definition of unilateralism in the British & World English dictionary