cower vs tremble

cower

verb
  • To crouch or cringe, or to avoid or shy away from something, in fear. 

  • To cause to cower; to frighten into submission. 

tremble

verb
  • To fear; to be afraid. 

  • To shake, quiver, or vibrate. 

noun
  • A shake, quiver, or vibration. 

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