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]

Moby Thesaurus II by Grady Ward, 1.0:

46 Moby Thesaurus words for "discredited":
   at a discount, belied, confounded, confuted, contested, deflated,
   denied, disbelieved, discarded, disgraced, dismissed, disproved,
   disputed, doubted, exploded, exposed, impugned, in Dutch, in bad,
   in bad odor, in bad repute, in discredit, in disfavor, in disgrace,
   in disrepute, invalidated, loaded with shame, mistrusted, moot,
   negated, negatived, out of countenance, out of favor, overthrown,
   overturned, punctured, questioned, refuted, rejected, shamed,
   shown up, suspect, suspected, under a cloud, under suspicion,
   upset