linchpin vs principle

linchpin

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

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. 

principle

verb
  • To equip with principles; to establish, or fix, in certain principles; to impress with any tenet or rule of conduct. 

noun
  • A fundamental essence, particularly one producing a given quality. 

  • A rule used to choose among solutions to a problem. 

  • A rule or law of nature, or the basic idea on how the laws of nature are applied. 

  • Bernoulli's Principle 

  • An original faculty or endowment. 

  • A fundamental assumption or guiding belief. 

  • A source, or origin; that from which anything proceeds; fundamental substance or energy; primordial substance; ultimate element, or cause. 

  • Moral rule or aspect. 

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