embolus vs encirclement

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. 

encirclement

noun
  • The act of encircling or the state of being encircled 

  • The isolation of a target by the formation of a blockade around it 

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