approbative vs facultative

approbative

adj
  • Sanctioning officially, giving authorization or approval to something. 

  • Expressing approval. 

noun
  • A word or grammatical form which denotes a positive affect expressing the appreciation or approval of the speaker. 

facultative

adj
  • That grants permission or power to do something. 

  • Able to perform a particular life function, or to live generally, in more than one way. 

  • Of or relating to faculty, especially to mental faculty. 

  • Not obligate; optional, discretionary or elective. 

  • At which a given function is positive. 

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