cryptic

Concise Oxford English Dictionary © 2008 Oxford University Press:
cryptic/ˈkrɪptɪk/

▶adjective

• 1 mysterious or obscure in meaning.

  ■ (of a crossword) having difficult clues which indicate the solutions indirectly.

• 2 Zoology (of coloration or markings) serving to camouflage an animal in its natural environment.

– derivatives
cryptically adverb.

– origin C17: from late L. crypticus, from Gk kruptikos, from kruptos ‘hidden’.