The Collaborative International Dictionary of English v.0.48:

Inaccuracy \In*ac"cu*ra*cy\, n.; pl. Inaccuracies.
   [1913 Webster]
   1. The quality of being inaccurate; lack of accuracy or
      exactness.
      [1913 Webster]

   2. That which is inaccurate or incorrect; mistake; fault;
      defect; error; as, in inaccuracy in speech, copying,
      calculation, etc.
      [1913 Webster]

WordNet (r) 3.0 (2006):

inaccuracy
    n 1: the quality of being inaccurate and having errors [ant:
         accuracy, truth]