nugatory vs unenforceable

nugatory

adj
  • Ineffective, invalid or futile. 

  • Having no force, inoperative, ineffectual. 

  • Trivial, trifling or of little importance. 

  • Removable from a computer program with safety, but harmless if retained. 

unenforceable

adj
  • Resistant to enforcement. 

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