of a piece vs unstable

of a piece

prep
  • Used other than figuratively or idiomatically: see of, a, piece. 

  • Of the same kind. 

unstable

verb
  • To release (an animal) from a stable. 

adj
  • Readily decomposable. 

  • Not stable. 

  • Radioactive, especially with a short half-life. 

  • Unpredictable. 

  • Fickle. 

  • Having a strong tendency to change. 

  • Fluctuating; not constant. 

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