em·bo·lus 
(ĕmbə-ləs)
(ĕmbə-ləs)n. pl. em·bo·li (-lī′)
A mass, such as an air bubble, a detached blood clot, or a foreign body, that travels through the bloodstream and lodges so as to obstruct or occlude a blood vessel.
[Latin, piston of a pump, from Greek embolos, stopper, plug, from emballein, to insert; see EMBLEM.]