secret Synonyms

hidden private clandestine privy secluded occult mystic cloak-and-dagger hole-and-corner concealed closed book confidential mystical underground hush-hush undercover unknown obscure covert enigma surreptitious mystery recondite mysterious handshake puzzler dirty laundry firsthand magic number unacknowledged unseen untold unnoticed withheld why visceral veiled back channel unfrequented stowaway stealthy stealthily stealthful stealth sphinx sneaky sneaking skulking stumper subterranean