diminution vs lessening

diminution

noun
  • A lessening, decrease or reduction. 

  • a compositional technique where the composer shortens the melody by shortening its note values. 

  • The act or process of making diminutive. 

lessening

noun
  • A growing lesser; reduction or decrease. 

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