Source : Webster's Revised Unabridged Dictionary (1913)

Indigestible \In`di*gest"i*ble\, a. [L. indigestibilis: cf. F.
   indigestible. See {In-} not, and {Digest}.]
   1. Not digestible; not readily soluble in the digestive
      juices; not easily convertible into products fitted for
      absorption.

   2. Not digestible in the mind; distressful; intolerable; as,
      an indigestible simile. --T. Warton. --
      {In`di*gest"i*ble*ness}, n. -- {In`di*gest"i*bly}, adv.

Source : WordNet®

indigestible
     adj : digested with difficulty [ant: {digestible}]