[1] : The Collaborative International Dictionary of English v.0.48

unintelligible \unintelligible\
   see intelligible.
see also:
intelligible 

[2] : WordNet (r) 2.0

unintelligible
     adj 1: poorly articulated or enunciated, or drowned by noise;
            "unintelligible speech" ant: intelligible
     2: not clearly understood or expressed syn: opaque
see also:
intelligible opaque 

[3] : Moby Thesaurus II by Grady Ward, 1.0

23 moby thesaurus words for "unintelligible":
   greek to one, ambiguous, amphibological, beyond understanding,
   equivocal, impenetrable, inarticulate, incognizable, incoherent,
   incomprehensible, inscrutable, numinous, opaque,
   past comprehension, rambling, tenebrous, uncertain, unclear,
   unconnected, unfathomable, unknowable, unsearchable, vague

[4] : Bouvier's Law Dictionary, Revised 6th Ed (1856)

unintelligible. that which cannot be understood. 
     2. when a law, a contract, or will, is unintelligible, it has no effect 
whatever. vide construction, and the authorities there referred to. 

Unintelligible >> U Words
Unintelligible, definition of term: Unintelligible
unintelligible_pag1.html