retain vs sustain

retain

verb
  • To keep in possession or use. 

  • To employ by paying a retainer. 

  • To hold back (a pupil) instead of allowing them to advance to the next class or year. 

  • To keep in one's pay or service. 

  • To hold secure. 

sustain

verb
  • To maintain, or keep in existence. 

  • To provide for or nourish. 

  • To encourage or sanction (something). 

  • To allow, accept, or admit (e.g. an objection or motion) as valid. 

  • To keep from falling; to bear; to uphold; to support. 

  • To confirm, prove, or corroborate; to uphold. 

  • To aid, comfort, or relieve; to vindicate. 

  • To experience or suffer (an injury, etc.). 

noun
  • A mechanism which can be used to hold a note, as the right pedal on a piano. 

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