break off vs sunder

break off

verb
  • To remove a piece from a whole by breaking or snapping 

  • To end abruptly, either temporarily or permanently. 

  • To end a relationship. 

sunder

verb
  • To break or separate or to break apart, especially with force. 

  • To part, separate. 

noun
  • a separation into parts; a division or severance 

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