fits and starts vs unfrequent

fits and starts

noun
  • Activity which is intermittent, variable in intensity, and prolonged by interruptions. 

unfrequent

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

verb
  • To stop frequenting; cease to frequent. 

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