grow vs strengthen

grow

verb
  • To develop, to mature. 

  • To appear or sprout. 

  • To become larger, to increase in magnitude. 

  • To undergo growth; to be present (somewhere) 

  • To cause or allow something to become bigger, especially to cultivate plants. 

  • To assume a condition or quality over time. 

strengthen

verb
  • To grow strong or stronger. 

  • To make strong or stronger; to add strength to; to increase the strength of; to fortify. 

  • To empower; to give moral strength to; to encourage; to enhearten. 

  • To reinforce, to add to, to support (someone or something) 

  • To substantiate; to corroborate (a belief, argument, etc.) 

  • To augment; to improve; to intensify. 

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