lengthy vs not long

lengthy

adj
  • Speaking or writing at length; long-winded. 

  • Having length; long and overextended, especially in time rather than dimension. 

  • a lengthy text 

not long

adv
  • Used other than figuratively or idiomatically: see not, long. 

  • Fairly recently. 

How often have the words lengthy and not long occurred in a corpus of books? (source: Google Ngram Viewer )