able, enigmatic, incalculable, incognizable, mysterious, puzzling, sealed, strange, unapparent, unapprehended, unascertained, uncharted, unclassified, undisclosed, undiscoverable, undiscovered, undivulged, unexplained, unexplored, unexposed, unfamiliar, unfathomed, unheard, unheard-of, unidentified, uninvestigated, unknowable, unknown, unperceived, unplumbed, unrevealed, unsuspected, untouched, virgin