The Collaborative International Dictionary of English v.0.48:

disabuse \dis`a*buse"\, v. t. [imp. & p. p. Disabused; p. pr.
   & vb. n. Disabusing.] [Pref. dis- + abuse; cf. F.
   d['e]sabuser.]
   To set free from mistakes; to undeceive; to disengage from
   fallacy or deception; to set right; -- often used with of;
   as, to disabuse one of his illusions.
   [1913 Webster]

         To undeceive and disabuse the people.    --South.
   [1913 Webster]

         If men are now sufficiently enlightened to disabuse
         themselves or artifice, hypocrisy, and superstition,
         they will consider this event as an era in their
         history.                                 --J. Adams.
   [1913 Webster]

WordNet (r) 3.0 (2006):

disabuse
    v 1: free somebody (from an erroneous belief)

The Devil's Dictionary (1881-1906):

DISABUSE, v.t.  The present your neighbor with another and better
error than the one which he has deemed it advantageous to embrace.