cumulate vs lessen

cumulate

verb
  • To accumulate; to amass. 

  • To be accumulated. 

adj
  • accumulated, agglomerated, amassed 

noun
  • An igneous rock formed by the accumulation of crystals from a magma either by settling or floating. 

lessen

conj
  • unless. 

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

  • To become less. 

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