degrade vs downgrade

degrade

verb
  • To lower in value or social position. 

  • To reduce in altitude or magnitude, as hills and mountains; to wear down. 

  • To reduce in quality or purity. 

downgrade

verb
  • To place lower in position. 

  • to reduce the official estimate of a storm's intensity. 

  • To reduce in complexity, or remove unnecessary parts; to dumb down. 

  • To revert software back to an older version. 

  • To disparage. 

noun
  • A reduction of a rating, as a financial or credit rating. 

  • A downhill gradient on a road or railway. 

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