clot 
(klŏt)
(klŏt)n.
1. A thick, viscous, or coagulated mass or lump, as of blood.
2. A clump, mass, or lump, as of clay.
3. A compact group: a clot of trucks blocking the tunnel's entrance.
v. clot·ted, clot·ting, clots
v.intr.
To form into a clot or clots; coagulate: The blood clotted over the wound.
v.tr.
1. To cause to form into a clot or clots.
2. To fill or cover with or as if with clots.
[Middle English, from Old English clott, lump.]