Other forms: clotting, clots, clotted
A clot is the thick lump that forms when blood sets. The body's way of plugging a leak.
It is essential when it happens in a wound and dangerous when it happens inside a vessel, which is why blood clots in the leg or the lung are medical emergencies. The verb is to clot, and blood clots on its own. Anticoagulants are drugs that stop it. British informal speech uses clot as a mild insult meaning a fool, which is affectionate rather than cutting.
Middle English
clot
English, today
clot
From Middle English clot. From Middle English clot, clotte, from Old English clott, from Proto-West Germanic klott (“lump”). Cognate with German Klotz (“block”). a doublet of clod and klutz.
Etymology from Wiktionary, CC BY-SA