embolus vs restriction

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. 

restriction

noun
  • A regulation or limitation that restricts. 

  • The act of restricting, or the state of being restricted. 

  • The mechanism by which a cell degrades foreign DNA material. 

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