lessen vs whittle

lessen

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

  • To become less. 

conj
  • unless. 

whittle

verb
  • To reduce or gradually eliminate something (such as a debt). 

  • To cut or shape wood with a knife. 

  • To make eager or excited; to excite with liquor; to inebriate. 

noun
  • A knife; especially, a pocket knife, sheath knife, or clasp knife. 

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