n. the presence or formation of a blood clot (thrombus) in a blood vessel, including vessels in the heart (coronary thrombosis). Thrombosis is likely to develop where blood flow is impeded by disease, injury, or a foreign substance. Formation of a blood clot in a vein is called venous thrombosis (see deep vein thrombosis). A thrombosis in the brain (cerebral thrombosis) can cause a thrombotic stroke or cerebrovascular accident. See also auditory thrombosis. —thromboticadj.