knop vs nub

knop

noun
  • A knob, usually ornamental 

nub

noun
  • A small lump or knob. 

  • a pointing stick 

  • The clitoris. 

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

verb
  • To push; to nudge. 

  • To beckon. 

  • To hit the ball weakly. 

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