decouple vs unclasp

decouple

verb
  • To unlink; to take or come apart. 

  • To muffle the seismic waves of (a nuclear explosion) by performing it underground. 

unclasp

verb
  • to separate from being clasped 

  • to become unfastened 

  • to release the clasp from something 

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