occasional vs unfrequent

occasional

adj
  • Occurring or appearing irregularly from time to time, but not often. 

  • Created for a specific occasion. 

  • Acting in the indicated role from time to time. 

  • Intended for use as the occasion requires. 

noun
  • A person who does something only occasionally. 

unfrequent

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

verb
  • To stop frequenting; cease to frequent. 

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