lessen vs prefer

lessen

verb
  • To make less; to diminish; to reduce. 

  • To become less. 

conj
  • unless. 

prefer

verb
  • To be in the habit of choosing something rather than something else; to favor; to like better. 

  • To present or submit (something) to an authority (now usually in "to prefer charges"). 

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