secret Synonyms

clandestine private hidden concealed privy covert hush-hush confidential secluded obscure undercover mysterious mystery underground mystic hole-and-corner personal unknown mystical enigma enigmatic closed book furtive occult cloak-and-dagger secretive stealthy unrevealed restricted recondite classified surreptitious handshake magic number veiled visceral stealthily why stealthful firsthand sneaky dirty laundry stealth puzzler withheld sphinx unnoticed unacknowledged back channel untold