intermittent vs unfrequent

intermittent

adj
  • Stopping and starting, occurring, or presenting at intervals; coming after a particular time span. 

  • Existing only for certain seasons; that is, being dry for part of the year. 

unfrequent

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

verb
  • To stop frequenting; cease to frequent. 

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