call off vs unite

call off

verb
  • To telephone in one's notice of a day's absence from work. 

  • To recall; to cancel or call a halt to. 

unite

verb
  • To bring together as one. 

  • To come together as one. 

noun
  • A British gold coin worth 20 shillings, first produced during the reign of King James I, and bearing a legend indicating the king's intention of uniting the kingdoms of England and Scotland. 

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