nonextant (adjective) gone: not present, no longer in existence
Sinonime: abstruseness, brainteaser, braintwister,
charade, chiller, cliffhanger, closed book, conundrum, crux, cryptogram,
difficulty,
enigma, grabber, inscrutability, inscrutableness, mindboggler, mystification,
occult,
oracle, perplexity, poser, problem, puzzlement, question, rebus, riddle, rune,
secrecy, sixty-four-thousand-dollar question, sphinx, stickler, stumper, subtlety, teaser, thriller, tough nut to crack, twister, whodunit, why*
Antonime: known,
understanding