The Collaborative International Dictionary of English v.0.48:

Discredit \Dis*cred"it\, v. t. [imp. & p. p. Discredited; p.
   pr. & vb. n. Discrediting.] [Cf. F. discr['e]diter.]
   1. To refuse credence to; not to accept as true; to
      disbelieve; as, the report is discredited.
      [1913 Webster]

   2. To deprive of credibility; to destroy confidence or trust
      in; to cause disbelief in the accuracy or authority of.
      [1913 Webster]

            An occasion might be given to the . . . papists of
            discrediting our common English Bible. --Strype.
      [1913 Webster]

   2. To deprive of credit or good repute; to bring reproach
      upon; to make less reputable; to disgrace.
      [1913 Webster]

            He. . . least discredits his travels who returns the
            same man he went.                     --Sir H.
                                                  Wotton.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

discredited \discredited\ adj.
   1. being brought into disrepute; as, a discredited
      politician.

   Syn: damaged.
        [WordNet 1.5]

   2. suffering shame.

   Syn: disgraced, dishonored, shamed.
        [WordNet 1.5]

   3. having been shown to be incorrect; as, a discredited
      theory or policy.
      [PJC]

WordNet (r) 3.0 (2006):

discredited
    adj 1: being unjustly brought into disrepute; "a discredited
           politician"; "her damaged reputation" [syn:
           discredited, damaged]
    2: suffering shame [syn: discredited, disgraced,
       dishonored, shamed]