stiffen vs sustain

stiffen

verb
  • To become stiff. 

  • To make stiff. 

sustain

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

  • To provide for or nourish. 

  • To encourage or sanction (something). 

  • To maintain, or keep in existence. 

  • 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. 

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

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