keystone vs linchpin

keystone

noun
  • Something on which other things depend for support. 

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

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

  • The combination of the shortstop and second baseman. 

  • The top stone of an arch. 

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%. 

linchpin

noun
  • A central cohesive source of stability and security; a person or thing that is critical to a system or organisation. 

  • A pin inserted through holes at the end of an axle or shaft, so as to secure a wheel or shaft-mounted device. 

verb
  • To adopt as, or serve as, a central cohesive source of stability and security. 

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