mighty vs tough proposition

mighty

adj
  • Excellent, extremely good. 

  • Very strong; possessing might. 

  • Very heavy and powerful. 

  • Accomplished by might; hence, extraordinary; wonderful. 

  • Very large; hefty. 

adv
  • Very; to a high degree. 

tough proposition

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