restriction vs retardant

restriction

noun
  • The act of restricting, or the state of being restricted. 

  • A regulation or limitation that restricts. 

  • The mechanism by which a cell degrades foreign DNA material. 

retardant

noun
  • Something that serves to retard (slow down) the action of something 

adj
  • Serving to impede (slow down) the action of something 

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