Coagulated blood; clotted blood; the viscous portion of blood that remains after serum is removed.
From Latin cruor meaning 'gore, blood,' related to crudus (raw, crude). The term entered English medical vocabulary in the 16th-17th centuries through Latin scientific terminology.
Before modern medicine understood blood cells and plasma, doctors used 'cruor' to distinguish the dark, clotted stuff from the lighter liquid part—it's a word frozen in time from when medicine was more observational than chemical!
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