undiscoverable

from WordNet (r) 3.0 (2006)

undiscoverable
    adj 1: not able to be ascertained; resisting discovery [syn:
           {unascertainable}, {undiscoverable}]

from The Collaborative International Dictionary of English v.0.48

Undiscoverable \Undiscoverable\
   See {discoverable}.

from Moby Thesaurus II by Grady Ward, 1.0

52 Moby Thesaurus words for "undiscoverable":
      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