petrify vs thicken

petrify

verb
  • To produce rigidity akin to stone. 

  • To make callous or obdurate; to stupefy; to paralyze; to transform; as by petrification. 

  • To become stone, or of a stony hardness, as organic matter by calcareous deposits. 

  • To harden organic matter by permeating with water and depositing dissolved minerals. 

  • To immobilize with fright. 

  • To become stony, callous, or obdurate. 

thicken

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

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

  • To become 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 petrify and thicken occurred in a corpus of books? (source: Google Ngram Viewer )