unknowable

from WordNet (r) 3.0 (2006)

unknowable
    adj 1: not knowable; "the unknowable mysteries of life" [ant:
           {cognisable}, {cognizable}, {cognoscible}, {knowable}]

from The Collaborative International Dictionary of English v.0.48

Unknowable \Unknowable\
   See {knowable}.

from Moby Thesaurus II by Grady Ward, 1.0

55 Moby Thesaurus words for "unknowable":
      Greek to one, able, ambiguous, arcane, beyond understanding,
      cabalistic, enigmatic, impenetrable, inarticulate, incalculable,
      incognizable, incoherent, incomprehensible, inscrutable,
      mysterious, mystic, numinous, past comprehension, puzzling,
      rambling, sealed, strange, unapparent, unapprehended,
      unascertained, unbeknown, uncharted, unclassified, unconnected,
      undisclosed, undiscoverable, undiscovered, undivulged, unexplained,
      unexplored, unexposed, unfamiliar, unfathomable, unfathomed,
      ungraspable, unguessed, unheard, unheard-of, unidentified,
      unimaginable, unintelligible, uninvestigated, unknown, unperceived,
      unplumbed, unrevealed, unsearchable, unsuspected, untouched,
      virgin