embolus

noun

1. An obstruction causing an embolism: a blood clot, air bubble or other matter carried by the bloodstream and causing a blockage or occlusion of a blood vessel.
2. The structure on the end of the palp of male arachnids which contains the opening to the ejaculatory duct.

   “Those spiders with a simple bulb insert most of this; those with a complex palp insert only the embolus, which in some species is very long […]”