get heavier vs thicken

get heavier

thicken

verb
  • To become thicker (in the sense of wider). 

  • To become thicker (in the sense of more viscous). 

  • To make thicker (in the sense of more viscous). 

  • To make thicker (in the sense of wider). 

  • To make more frequent. 

  • To strengthen; to confirm. 

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