deepen vs quieten

deepen

verb
  • To become lower in tone 

  • To make deep or deeper 

  • To make more sound or heavy. 

  • To make darker or more intense; to darken 

  • To become deeper 

  • To become more intimate. 

  • To make lower in tone 

  • To become darker or more intense 

  • To become more thorough or extensive. 

  • To make more thorough or extensive. 

  • To become more sound or heavy. 

  • To make more intimate. 

  • To make more poignant or affecting; to increase in degree 

quieten

verb
  • To become quiet. 

  • To make quiet. 

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