decouple vs unloosen

decouple

verb
  • To unlink; to take or come apart. 

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

unloosen

verb
  • To unloose; to loosen. 

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