buttress vs underpinning

buttress

noun
  • A brick or stone structure built against another structure to support it. 

  • Anything that supports or strengthens. 

  • A buttress-root. 

  • Anything that serves to support something; a prop. 

  • A feature jutting prominently out from a mountain or rock. 

verb
  • To support something or someone by supplying evidence. 

  • To support something physically with, or as if with, a prop or buttress. 

underpinning

noun
  • A support or foundation, especially as a structure of masonry that supports a wall. 

  • The lower body or legs. 

  • A basis for something. 

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