arcane, cabalistic, censored, classified, close, closed, concealed, cryptic, dark, echoless, enigmatic, esoteric, hermetic, hidden, hush as death, hush-hush, hushed, implicit, implied, inaudible, inferred, latent, mousy, mysterious, noiseless, occult, quiescent, quiet, restricted, secret, silent, smothered, soundless, stifled, still, still as death, stilly, subaudible, suppressed, tacit, top secret, ulterior, unarticulated, unbreatheable, undeclared, under security, under wraps, understood, undisclosable, undisclosed, undivulgable, undivulged, unexpressed, unhearable, unmentioned, unproclaimed, unpronounced, unpublished, unrecorded, unrevealable, unrevealed, unsaid, unsounded, unspoken, unsung, untalked-of, untellable, untold, unutterable, unvocalized, unvoiced, unwhisperable, unwritten, whist, wordless