WordNet (r) 3.0 (2006):

oversimplification
    n 1: an act of excessive simplification; the act of making
         something seem simpler than it really is [syn:
         oversimplification, simplism]
    2: a simplification that goes too far (to the point of
       misrepresentation) [syn: oversimplification, simplism]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "oversimplification":
   callowness, coarseness, conceptual crudity, crudeness, crudity,
   greenness, immatureness, immaturity, nondevelopment,
   oversimplicity, oversimplifying, rawness, reductionism,
   reductivism, roughness, rudeness, simplism, the rough,
   uncultivation, undevelopment, unfinish, unfinishedness,
   unfledgedness, unrefinement, unripeness