Synonyms and related words :
arcane, bated, cabalistic, censored, classified, close, closed, concealed, crushed, cryptic, damped, dampened, dark, dead, deadened, dull, dulled, enigmatic, esoteric, flat, hermetic, hidden, hush-hush, latent, muffled, muted, mysterious, occult, quashed, quelled, repressed, restricted, secret, smashed, softened, sordo, squashed, squelched, stifled, subdued, suffocated, suppressed, top secret, ulterior, unbreatheable, under security, under wraps, undisclosable, undisclosed, undivulgable, undivulged, unrevealable, unrevealed, unspoken, untellable, untold, unutterable, unuttered, unwhisperable