cultivate vs refine

cultivate

verb
  • To nurture; to foster; to tend. 

  • To turn or stir soil in preparation for planting. 

  • To grow plants, notably crops. 

refine

verb
  • To make nice or subtle. 

  • To improve in accuracy, delicacy, or excellence. 

  • To become pure; to be cleared of impure matter. 

  • To purify of coarseness, vulgarity, inelegance, etc.; to polish. 

  • To purify; reduce to a fine, unmixed, or pure state; to free from impurities. 

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