criterion vs linchpin

criterion

noun
  • A standard or test by which individual things or people may be compared and judged. 

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 criterion and linchpin occurred in a corpus of books? (source: Google Ngram Viewer )