rigidity vs toughness

rigidity

noun
  • Stiffness of appearance or manner; want of ease or elegance. 

  • stickiness (of prices/wages etc.). Describing the tendency of prices and money wages to adjust to changes in the economy with a certain delay. 

  • The quality or state of being rigid; lack of pliability; the quality of resisting change of physical shape 

  • The amount of resistance with which a body opposes change of form. 

toughness

noun
  • Fortitude; hardiness; mettle. 

  • A formidable difficulty. 

  • Resistance to fracture when stressed, or the degree of such resistance. 

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