lessening vs waning

lessening

noun
  • A growing lesser; reduction or decrease. 

waning

noun
  • The fact or act of becoming smaller. 

  • The fact or act of becoming less or less intense or present; fading. 

adj
  • Becoming weaker or smaller. 

  • Of the lunar phase: as it shrinks when viewed from the Earth. 

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