uncommon vs unfrequent

uncommon

adj
  • Rare; not readily found; unusual. 

  • Remarkable; exceptional. 

unfrequent

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

verb
  • To stop frequenting; cease to frequent. 

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