castoff vs riddance

castoff

noun
  • Something that has been rejected or discarded; a reject. 

adj
  • discarded, rejected. 

riddance

noun
  • The act of being rid of something; deliverance 

  • The earth thrown up by a burrowing animal. 

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