Source : Webster's Revised Unabridged Dictionary (1913)

Incomprehensible \In*com`pre*hen"si*ble\, a. [L.
   incomprehensibilis: cf. F. incompr['e]hensible. See {In-}
   not, and {Comprehensible}.]
   1. Not capable of being contained within limits.

            An infinite and incomprehensible substance.
                                                  --Hooker.

   2. Not capable of being comprehended or understood; beyond
      the reach of the human intellect; inconceivable.

            And all her numbered stars that seem to roll Spaces
            incomprehensible.                     --Milton.
      -- {In*com`pre*hen"si*ble*ness}, n. --
      {In*com`pre*hen"si*bly}, adv.

Source : WordNet®

incomprehensible
     adj 1: incapable of being explained or accounted for; "inexplicable
            errors"; "left the house at three in the morning for
            inexplicable reasons" [syn: {inexplicable}] [ant: {explicable}]
     2: difficult to understand; "the most incomprehensible thing
        about the universe is that it is comprehensible"- A.
        Einstein [syn: {uncomprehensible}] [ant: {comprehensible}]