hir·u·din 
(hîr-dn, hîrə-dən, -yə-)
(hîr-dn, hîrə-dən, -yə-)n.
A substance secreted by the buccal glands of leeches, capable of preventing coagulation by inactivating thrombin and used in medicine as an anticoagulant.
[Originally a trademark, from Latin hirūdō, leech.]