define thromboplastin
Definition of THROMBOPLASTIN. : a complex enzyme found especially in platelets that functions in the conversion of prothrombin into thrombin in the clotting of blood. ADVERTISEMENT. International Scientific Vocabulary, from thromboplastic.First Known Use: 1911. a complex enzyme that is found in brain, lung, and other tissues and especially in blood platelets and that functions in the conversion of prothrombin to thrombin in the clotting of bloodâcalled also thrombokinase.