The Collaborative International Dictionary of English v.0.48:

Intelligibility \In*tel`li*gi*bil"i*ty\, [Cf. F.
   intelligilibilit['e].]
   The quality or state of being intelligible; clearness;
   perspicuity; definiteness.
   [1913 Webster]

WordNet (r) 3.0 (2006):

intelligibility
    n 1: the quality of language that is comprehensible [ant:
         unintelligibility]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "intelligibility":
   clarity, clear coast, clear road, ease, easiness, easy going,
   effortlessness, expressiveness, facileness, facility, freedom,
   highroad, interpretability, lack of hindrance, meaningfulness,
   meatiness, pithiness, plain sailing, plane sailing, pregnancy,
   readability, royal road, sententiousness, significance,
   significancy, significantness, simplicity, smooth road,
   smooth sailing, smoothness, straight sailing, suggestiveness,
   uncomplexity, uncomplicatedness