antiviral Syllabification: (an·ti·vi·ral)Pronunciation: /ˌantēˈvīrəl, ˌantī-/Definition of antiviral adjective 1 Medicine (chiefly of a drug or treatment) effective against viruses. 2 Computing (of software) designed to detect, remove, or offer protection against computer viruses. noun Medicine an antiviral drug or medicine. antiviral in other Oxford dictionaries Definition of antiviral in the British & World English dictionary