bioassay Syllabification: (bi·o·as·say)Pronunciation: /ˌbīōəˈsā, -ˈasā/Definition of bioassay noun measurement of the concentration or potency of a substance by its effect on living cells or tissues. Origin: early 20th century: from bio- 'life' + assaybioassay in other Oxford dictionaries Definition of bioassay in the British & World English dictionary