The Collaborative International Dictionary of English v.0.48:

Misapprehension \Mis*ap`pre*hen"sion\, n.
   A mistaking or mistake; wrong apprehension of one's meaning
   of a fact; misconception; misunderstanding.
   [1913 Webster]

WordNet (r) 3.0 (2006):

misapprehension
    n 1: an understanding of something that is not correct; "he
         wasn't going to admit his mistake"; "make no mistake about
         his intentions"; "there must be some misunderstanding--I
         don't have a sister" [syn: mistake, misunderstanding,
         misapprehension]