embolus vs thrombus

embolus

noun
  • 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. 

  • The structure on the end of the palp of male arachnids which contains the opening to the ejaculatory duct. 

thrombus

noun
  • A blood clot formed from platelets and other elements that forms in a blood vessel in a living organism, and causes thrombosis or obstruction of the vessel at its point of formation or travel to other areas of the body. 

How often have the words embolus and thrombus occurred in a corpus of books? (source: Google Ngram Viewer )