fettering vs obstruction

fettering

noun
  • The act by which something is fettered or constricted. 

obstruction

noun
  • The act of obstructing, or state of being obstructed. 

  • Something which obstructs or impedes, either intentionally or unintentionally 

  • The condition of having the natural powers obstructed in their usual course; the arrest of the vital functions; death. 

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