frighten vs tremble

frighten

verb
  • To cause to feel fear; to scare; to cause to feel alarm or fright. 

tremble

verb
  • To fear; to be afraid. 

  • To shake, quiver, or vibrate. 

noun
  • A shake, quiver, or vibration. 

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