What does clot mean?
A clot is a semi-solid mass that forms when a liquid — most importantly blood — coagulates. In the body, clotting is an essential protective process: when a vessel is injured, platelets and fibrin gather to form a clot that seals the wound and stops bleeding. Clots become dangerous when they form where they are not needed, obstructing vessels and potentially causing deep vein thrombosis, pulmonary embolism, heart attack, or stroke. The word also carries a colloquial meaning in British English, where 'clot' informally describes a foolish or bungling person. Medical writing uses the term neutrally and precisely, often distinguishing a clot that forms in place (a thrombus) from one that travels through the bloodstream (an embolus). Anticoagulant drugs such as heparin and warfarin work by preventing or dissolving clots, making the word central to everyday discussions of cardiovascular medicine.
A thickened, semi-solid mass formed by the coagulation of blood or another liquid.
"A small clot formed at the site of the injection."
In medical contexts, a clot that forms within a vessel is called a thrombus.
(British, informal) A stupid or clumsy person.
"He's a lovable old clot who can never find his keys."
This sense is chiefly British and mildly derogatory.
Standard plural; used freely in both medical and informal contexts.
"Several small clots were visible on the scan."
Without the humble blood clot, a single paper cut could bleed you dry — yet the same life-saving mechanism, misplaced, causes most heart attacks and strokes.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of clot
The word 'clot' derives from Middle English, likely influenced by or related to Old English 'clott' meaning a lump or mass, with possible reinforcement from Middle Dutch cognates such as 'klot' (lump, ball). It originally referred to any rounded lump or congealed mass before becoming especially associated with coagulated blood. Related Germanic forms appear across Dutch and German, reflecting a shared Germanic root for lumpy or rounded masses.
Related word forms
How clot is actually used
The medical sense is neutral and standard in both British and American English. The informal British sense meaning a stupid person is mildly derogatory and largely confined to British usage.
Easily confused with clot
A clog is an obstruction of any kind (or a wooden shoe), while a clot specifically refers to a coagulated mass of blood or another liquid.
Coagulate is the verb describing the process of forming a clot, whereas clot names the resulting mass itself.