plausible vs unallowable

plausible

adj
  • Obtaining approbation; specifically pleasing; apparently right; specious. 

  • Seemingly or apparently valid, likely, or acceptable; conceivably true or likely. 

unallowable

adj
  • Not allowable 

  • For which an allowance may not be claimed 

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