* Thromb- This is the core root word meaning "clotting" or "clot." You'll find it in words like thrombosis (formation of a blood clot), thrombocyte (a blood platelet), and thrombolytic (dissolving a clot).
* Coagul- This root word also means "clotting" or "coagulation," the process of blood thickening. Examples include coagulant (a substance that promotes clotting) and coagulase (an enzyme that helps clot blood).
* Hem- This root word means "blood." While related to clotting, it doesn't specifically describe the act of clotting itself.
Therefore, the root word that does not describe a form of clotting is "hem." It refers to blood in general.