interloping vs obstruction

interloping

noun
  • An act of intrusion or encroachment. 

  • Illegal Indian trade within the area over which the Hudson's Bay Company held a trade monopoly. 

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 interloping and obstruction occurred in a corpus of books? (source: Google Ngram Viewer )