The Collaborative International Dictionary of English v.0.48:

Indeterminable \In`de*ter"mi*na*ble\, a. [L. indeterminabilis:
   cf. F. ind['e]terminable. See In- not, and Determine.]
   Not determinable; impossible to be determined; not to be
   definitely known, ascertained, defined, or limited. --
   In`de*ter"mi*na*bly, adv.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Indeterminable \In`de*ter"mi*na*ble\, n.
   An indeterminable thing or quantity. --Sir T. Browne.
   [1913 Webster]

WordNet (r) 3.0 (2006):

indeterminable
    adj 1: not capable of being definitely decided or ascertained
           [syn: indeterminable, undeterminable] [ant:
           determinable]
    2: incapable of being definitely ascertained