Entry 2 senses · 2 variants Webster, 1913 bioassay · IPA n. v. 01 n. appraisal of the biological activity of a substance by testing its effect on an organism. 1. appraisal of the biological activity of a substance by testing its effect on an organism. 02 v. to subject to a bio-assay. 1. to subject to a bio-assay. Syn. bio-assay.