reflux vs retrocede

reflux

verb
  • To flow back or return. 

  • To boil a liquid in a vessel having a reflux condenser 

noun
  • A technique, using a reflux condenser, allowing one to boil the contents of a vessel over an extended period. 

  • The backwards flow of any fluid. 

  • The leaking of stomach acid up into the oesophagus. 

retrocede

verb
  • To go back. 

  • To grant back. 

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