unfrequent vs unlikely

unfrequent

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

verb
  • To stop frequenting; cease to frequent. 

unlikely

adj
  • Not likely; improbable; not to be reasonably expected. 

  • Not holding out a prospect of success; likely to fail; unpromising. 

noun
  • Something or somebody considered unlikely. 

adv
  • In an improbable manner. 

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