immunoassay noun 1verb 1forms 3 noun1 •A test for the presence of a substance using the reaction of an antibody to its antigen, making use of the high selectivity of components of biological immune systems.An over-the-counter, pee-on-a-stick pregnancy test is an immunoassay. — 2016 verb1 •To carry out such a test. formsimmunoassayed · immunoassaying · immunoassays