foundation stone vs keystone

foundation stone

noun
  • A stone laid during the construction of a (usually important) building, the laying of which is usually marked by a ceremony. 

  • The basis of something. 

keystone

noun
  • The top stone of an arch. 

  • A retail price that is double the cost price; a markup of 100%. 

  • A native or resident of the American state of Pennsylvania. 

  • Something on which other things depend for support. 

  • The combination of the shortstop and second baseman. 

verb
  • To distort (an image) by projecting it onto a surface at an angle, which for example causes a square to look like a trapezoid. 

  • To double the cost price in order to determine the retail price; to apply a markup of 100%. 

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