entanglement vs knotty question

entanglement

noun
  • An obstruction of cables and spars across a river or harbour entrance. 

  • The condition of being deeply involved and intricated (with politics, a group, another person, etc.) 

  • The condition, or an instance, of being romantically or sexually involved with another person; an affair. 

  • The act of entangling. 

  • An obstruction placed in front or on the flank of a fortification, to impede an enemy's approach. 

knotty question

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