1. Mysterious in meaning; puzzling; ambiguous
2. Involving or using cipher, code, etc.
3. Zoology: Fitted for concealing; serving to camouflage
This word dates to the 1630's as "hidden, occult, mystical" from Latin Latin crypticus. Crypticus was a borrowing from Greek kryptikos ("fit for concealing"), which derives from kryptos ("hidden"). Kryptos ultimately derives from Proto-Indo-European *krau- ("to conceal, hide") and is the forebear of crypt.
Anyone else remember The Crypt Keeper from Tales from the Crypt? He scared the pants off me when I was a kid.