Source : Webster's Revised Unabridged Dictionary (1913)

Discreditable \Dis*cred"it*a*ble\, a.
   Not creditable; injurious to reputation; disgraceful;
   disreputable. -- {Dis*cred"it*a*bly}, adv.

Source : WordNet®

discreditable
     adj : tending to bring discredit or disrepute; blameworthy; "his
           marks were not at all discreditable"