linchpin vs nub

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. 

nub

noun
  • The essence or core of an issue, argument etc. 

  • a pointing stick 

  • The clitoris. 

  • A small lump or knob. 

verb
  • To push; to nudge. 

  • To beckon. 

  • To hit the ball weakly. 

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