refresher vs strengthener

refresher

noun
  • An equity grant given by a company to an existing employee, as opposed to an initial grant given to new employees. 

  • A review to refresh or renew knowledge. 

  • A fee paid to counsel to continue with a case, especially one that was adjourned. 

  • Something that refreshes. 

strengthener

noun
  • One who, or that which, gives or adds strength. 

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