The Collaborative International Dictionary of English v.0.48:

Misunderstand \Mis*un`der*stand"\
   (m[i^]s*[u^]n`d[~e]r*st[a^]nd"), v. t. [imp. & p. p.
   Misunderstood (m[i^]s*[u^]n`d[~e]r*st[oo^]d"); p. pr. & vb.
   n. Misunderstanding.]
   To misconceive; to mistake; to miscomprehend; to take in a
   wrong sense.
   [1913 Webster]

WordNet (r) 3.0 (2006):

misunderstand
    v 1: interpret in the wrong way; "Don't misinterpret my comments
         as criticism"; "She misconstrued my remarks" [syn:
         misconstrue, misinterpret, misconceive,
         misunderstand, misapprehend, be amiss]