The Collaborative International Dictionary of English v.0.48:
discreditable \dis*cred"it*a*ble\, a. Not creditable; injurious to reputation; disgraceful; disreputable. -- Dis*cred"it*a*bly, adv. [1913 Webster]WordNet (r) 3.0 (2006):
discreditable adj 1: tending to bring discredit or disrepute; blameworthy; "his marks were not at all discreditable"