maintain vs tremble

maintain

verb
  • To declare or affirm (a clause) to be true; to assert. 

  • To keep up; to preserve; to uphold (a state, condition etc.). 

tremble

noun
  • A shake, quiver, or vibration. 

verb
  • To shake, quiver, or vibrate. 

  • To fear; to be afraid. 

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