embolus
n.,
pl. 3li$ 73lj$8 5ModL < Gr embolos, anything put in, wedge < emballein < en3, in + ballein, to throw: see BALL26 any foreign matter, as a blood clot or air bubble, carried in the bloodstream and capable of causing an embolism

My grandmother died of a pulmonary embolus. Over a hundred years ago, it had not been learned that
it was extremely undesirable to keep women in bed for weeks after childbirth. The sluggish flow in deep
leg veins can promote formation of a rubbery clot the size of a small eel, which is at first attached to
the vein wall, but can become detached and go up the vena cava into right auricle and completely
block it, causing pain and sudden death.
Recently there have been warnings that passengers in economy seats on long airplane flights
may have lesser but serious problems.