The Collaborative International Dictionary of English v.0.48:

Untold \Un*told"\, a.
   1. Not told; not related; not revealed; as, untold secrets.
      [1913 Webster]

   2. Not numbered or counted; as, untold money.
      [1913 Webster]

WordNet (r) 3.0 (2006):

untold
    adj 1: of an incalculable amount; "untold suffering"

Moby Thesaurus II by Grady Ward, 1.0:

132 Moby Thesaurus words for "untold":
   all-comprehensive, all-inclusive, arcane, at issue, boundless,
   cabalistic, censored, classified, close, closed, concealed,
   conditional, conditioned, contingent, countless, cryptic, dark,
   dependent, depending, endless, enigmatic, enormous, esoteric,
   eternal, exhaustless, extending everywhere, gigantic, hermetic,
   hidden, hush-hush, illimitable, illimited, immeasurable, immense,
   in question, in suspense, in the balance, incalculable,
   incomprehensible, inconceivable, indescribable, inexhaustible,
   inexpressible, infinite, infinitely continuous, innumerable,
   interminable, interminate, latent, limitless, mammoth, measureless,
   mighty, monstrous, myriad, mysterious, no end of, numberless,
   occult, open, pendent, pending, perpetual, private, prodigious,
   restricted, secret, shoreless, silent, smothered, stifled, sumless,
   suppressed, suspenseful, termless, titanic, top secret, ulterior,
   unbounded, unbreatheable, uncircumscribed, uncountable, uncounted,
   undecided, undeclared, under security, under wraps, undetermined,
   undisclosable, undisclosed, undivulgable, undivulged,
   unestablished, unexpressed, unfathomable, unfixed, unimaginable,
   universal, unlimited, unmeasurable, unmeasured, unmentioned,
   unnumbered, unplumbed, unproclaimed, unpronounced, unpublished,
   unrecorded, unreported, unrevealable, unrevealed, unsaid,
   unsettled, unspeakable, unspoken, unsung, untalked-of, untellable,
   unthinkable, unutterable, unuttered, unvoiced, unwhisperable,
   unwritten, up for grabs, vast, without bound, without end,
   without limit, without measure, without number, wordless