Synonyms and related words :
able, beyond reach, closed forever to, closed to, enigmatic, impenetrable, impervious, inaccessible, incalculable, incognizable, lost to, mysterious, out of reach, puzzling, sealed, strange, un-come-at-able, unaccessible, unapparent, unapprehended, unapproachable, unascertained, unattainable, unavailable, unbeknown, uncharted, unclassified, undisclosed, undiscovered, undivulged, unexplained, unexplored, unexposed, unfamiliar, unfathomed, ungettable, unheard, unheard-of, unidentified, uninvestigated, unknowable, unknown, unobtainable, unperceived, unplumbed, unprocurable, unreachable, unrevealed, unsecurable, unsuspected, untouched, virgin