Secret

Synonyms Confidential, top secret, restricted, undisclosed, untold, uncommunicated, under wraps, off the record, not to be disclosed, hush-hush, hidden, camouflaged, unnoticeable, inconspicuous, covert, underground, conspiratorial, stealthy, hole-and-corner, sneaky, underhand, furtive, cryptic, coded, mysterious, recondite, esoteric, secluded, sheltered, unfrequented, lonely, out of the way, isolated, tucked away, strictly confidential, classified, unrevealed, unpublished, unknown, behind someone's back, unofficial, not to be made public, sub rosa, mum, concealed, disguised, invisible, clandestine, undercover, shrouded, surreptitious, cloak-and-dagger, closet, sly, shifty, black, encoded, enciphered, abstruse, arcane, cabbalistic, private, undisturbed, solitary, sequestered, remote, off the beaten track, and cut-off.

Synonyms Clandestine, undercover, hidden, conspiratorial, stealthy, hole-and-corner, sneaky, underhand, furtive, hush-hush, covert, underground, shrouded, surreptitious, cloak-and-dagger, closet, sly, shifty, and black.

Synonyms Uncommunicative, unforthcoming, private, taciturn, non-communicative, tight-lipped, close, reserved, introverted, discreet, secretive, reticent, media-shy, silent, quiet, close-mouthed, clamlike, introvert, and self-contained.

Synonyms Confidential matter, private affair, skeleton in the closet, confidence, skeleton in the cupboard, and secret.

Synonyms Mystery, problem, puzzle, poser, question, enigma, paradox, conundrum, riddle, and question mark.

Synonyms Recipe, blueprint, key, solution, formula, magic formula, and answer.