The Collaborative International Dictionary of English v.0.48:

Incalculable \In*cal"cu*la*ble\, a. [Pref. in- not + calculable:
   cf. F. incalculable.]
   Not capable of being calculated; beyond calculation; very
   great; as, his action did incalculable harm. --
   In*cal"cu*la*ble*ness, n. -- In*cal"cu*la*bly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

incalculable
    adj 1: not capable of being computed or enumerated [ant:
           calculable]

Moby Thesaurus II by Grady Ward, 1.0:

111 Moby Thesaurus words for "incalculable":
   able, agnostic, all-comprehensive, all-inclusive, ambiguous,
   boundless, capricious, chancy, changeable, countless, dicey,
   doubting, endless, enigmatic, equivocal, erratic, eternal,
   exhaustless, extending everywhere, fickle, hesitant, hesitating,
   illimitable, illimited, immeasurable, immense, incognizable,
   incomprehensible, indecisive, indemonstrable, inestimable,
   inexhaustible, infinite, infinitely continuous, innumerable,
   interminable, interminate, irresolute, limitless, measureless,
   mysterious, no end of, numberless, perpetual, polysemous, puzzling,
   sealed, shoreless, skeptical, strange, sumless, surreptitiously,
   termless, touch-and-go, unaccountable, unapparent, unapprehended,
   unascertained, unbeknown, unbounded, uncertain, uncharted,
   uncircumscribed, unclassified, unconfirmable, unconvinced,
   uncountable, uncounted, undisclosed, undiscoverable, undiscovered,
   undivinable, undivulged, unexplained, unexplored, unexposed,
   unfamiliar, unfathomable, unfathomed, unforeseeable, unheard,
   unheard-of, unidentified, uninvestigated, universal, unknowable,
   unknown, unlimited, unmeasurable, unmeasured, unnumbered,
   unperceived, unpersuaded, unplumbed, unpredictable, unprovable,
   unrevealed, unsure, unsuspected, untold, untouched, unverifiable,
   variable, virgin, wavering, whimsical, without bound, without end,
   without limit, without measure, without number