insufficient vs unfrequent

insufficient

adj
  • Not sufficient; of a type or kind that does not suffice, that does not satisfy requirements or needs. 

  • Not sufficient; lacking competent power or ability; unqualified, unequal, unfit. 

det
  • An inadequate quantity of; not enough. 

  • A quantity (of something) that is less than is needed. 

unfrequent

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

verb
  • To stop frequenting; cease to frequent. 

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