Synonyms and related words :
arcane, cabalistic, censored, clandestine, classified, close, closed, concealed, covert, cryptic, dark, enigmatic, esoteric, hermetic, hidden, hugger-mugger, hugger-muggery, hush, latent, mysterious, occult, restricted, secret, secretiveness, secretness, silence, smothered, stifled, suppressed, top secret, ulterior, unbreatheable, under security, under wraps, under-the-table, undisclosable, undisclosed, undivulgable, undivulged, unrevealable, unrevealed, unspoken, untellable, untold, unutterable, unuttered, unwhisperable