Synonyms and related words :
arcane, awesome, awful, cabalistic, censored, classified, close, closed, concealed, cryptic, dark, divine, enigmatic, esoteric, heavenly, hermetic, hidden, holy, hush-hush, incommunicable, inconceivable, incredible, indefinable, indescribable, ineffable, inenarrable, inexpressible, innominable, inviolable, inviolate, latent, marvelous, mysterious, noncommunicable, numinous, occult, prodigious, religious, restricted, sacred, sacrosanct, secret, smothered, spiritual, stifled, suppressed, top secret, ulterior, unbelievable, unbreatheable, undefinable, under security, under wraps, undisclosable, undisclosed, undivulgable, undivulged, unimaginable, unmentionable, unnameable, unrevealable, unrevealed, unspeakable, unspoken, untellable, untold, untouchable, unuttered, unwhisperable, venerable, wonderful, wondrous