a substance found in the salivary glands of leeches that prevents the coagulation of blood
See hirudin in American Heritage Dictionary 4
(hîr-o͞odˈn, hîrˈə-dən, -yə-)
noun
A substance secreted by the buccal glands of leeches, capable of preventing coagulation by inactivating thrombin and used in medicine as an anticoagulant.