depressing vs lightening

depressing

adj
  • Causing a reduction in economic activity. 

  • Causing depression or sadness. 

lightening

noun
  • The removal of cargo (especially crude oil) from a vessel in order to reduce its draft 

  • The sensation caused by the descent of the uterus into the pelvic cavity before the onset of labour 

  • The act or result of making something light or lighter. 

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