buttress vs flying buttress

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. 

flying buttress

noun
  • A buttress that stands apart from the structure that it supports, and is connected to it by an arch (flyer). 

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