enslavement vs entombment

enslavement

noun
  • The act of enslaving or the state of being a slave; bondage 

entombment

noun
  • The act of entombing or the state of being entombed 

  • The decommissioning of a radioactive site by encasing it in concrete 

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