Source : Webster's Revised Unabridged Dictionary (1913)

Intelligible \In*tel"li*gi*ble\, [L. intellegibilis: cf. F.
   intelligible. See {Intelligent}.]
   Capable of being understood or comprehended; as, an
   intelligible account or description; intelligible
   pronunciation, writing, etc.

         The intelligible forms of ancient poets. --Coleridge.

   Syn: Comprehensible; perspicuous; plain; clear.

Source : WordNet®

intelligible
     adj 1: capable of being apprehended or understood [syn: {apprehensible},
             {graspable}, {perceivable}, {understandable}]
     2: well articulated or enunciated, and loud enough to be heard
        distinctly; "intelligible pronunciation" [ant: {unintelligible}]