inconceivable vs unfrequent

inconceivable

adj
  • Unable to be conceived or imagined; unbelievable. 

unfrequent

verb
  • To stop frequenting; cease to frequent. 

adj
  • Not frequent; not common; not happening often; infrequent. 

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