The Collaborative International Dictionary of English v.0.48:

Dishonorable \Dis*hon"or*a*ble\, a. [Cf. F. d['e]shonorable.]
   1. Wanting in honor; not honorable; bringing or deserving
      dishonor; staining the character, and lessening the
      reputation; shameful; disgraceful; base.
      [1913 Webster]

   2. Wanting in honor or esteem; disesteemed.
      [1913 Webster]

            He that is dishonorable in riches, how much more in
            poverty!                              --Ecclus. x.
                                                  31.
      [1913 Webster]

            To find ourselves dishonorable graves. --Shak.
      -- Dis*hon"or*a*ble*ness, n. -- Dis*hon"or*a*bly, adv.
      [1913 Webster]

WordNet (r) 3.0 (2006):

dishonorable
    adj 1: lacking honor or integrity; deserving dishonor;
           "dishonorable in thought and deed" [syn: dishonorable,
           dishonourable] [ant: honorable, honourable]
    2: deceptive or fraudulent; disposed to cheat or defraud or
       deceive [syn: dishonest, dishonorable] [ant: honest,
       honorable]