I cannot think of an instance where blood clot could be an adjective. If you're talking about the action of blood clotting than that is a verb, and if you're referring to this is the past you could say "the blood clotted" but that is still not an adjective and sounds somewhat awkward. Clot (noun) - a coagulated mass, or substance adhering together Clot (verb) - to become or form a clot (clotted, clotting)
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