natural deposit (noun) natural resource: resource from the earth
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