cryptic vs hard to understand

cryptic

noun
  • A cryptic crossword puzzle. 

adj
  • Involving use of a code or cipher. 

  • Apparently identical, but actually genetically distinct. 

  • Serving as camouflage. 

  • Living in a cavity or small cave. 

  • Well camouflaged; having good camouflage. 

  • Mystified or of an obscure nature. 

  • Having hidden (unapparent) meaning. 

  • Of a crossword puzzle, or a clue in such a puzzle, using, in addition to definitions, wordplay such as anagrams, homophones and hidden words to indicate solutions. 

hard to understand

How often have the words cryptic and hard to understand occurred in a corpus of books? (source: Google Ngram Viewer )