able, arcane, cabalistic, censored, classified, close, closed, concealed, cryptic, dark, enigmatic, esoteric, hermetic, hidden, hush-hush, incalculable, incognizable, invisible, latent, mysterious, occult, puzzling, restricted, sealed, secret, smothered, stifled, strange, suppressed, top secret, ulterior, unapparent, unapprehended, unascertained, unbeknown, unbreatheable, uncharted, unclassified, under security, under wraps, undetected, undisclosable, undiscoverable, undiscovered, undivulgable, undivulged, unexplained, unexplored, unexposed, unfamiliar, unfathomed, unheard, unheard-of, unidentified, uninvestigated, unknowable, unknown, unperceived, unplumbed, unrevealable, unrevealed, unseen, unsolved, unspied, unspoken, unsuspected, untellable, untold, untouched, untraced, untracked, unutterable, unuttered, unwhisperable, virgin