bioavailability Syllabification: (bi·o·a·vail·a·bil·i·ty)Pronunciation: /ˌbīōˌəvāləˈbilitē/Definition of bioavailability noun Physiology the proportion of a drug or other substance that enters the circulation when introduced into the body and so is able to have an active effect. Derivatives bioavailablePronunciation: /-əˈvāləbəl/ adjective bioavailability in other Oxford dictionaries Definition of bioavailability in the British & World English dictionary