WordWeb Online

1. Lacking honor or integrity; deserving dishonor
   "dishonorable in thought and deed";
   - dishonourable [Brit, Cdn]
    
2. Deceptive or fraudulent; disposed to cheat or defraud or deceive
   - dishonest, dishonourable [Brit, Cdn]

See also: ambidextrous, beguiling, bent [Brit, informal], black, blackguardly, corrupt, crooked [informal], debasing, deceitful, deceptive, degrading, disgraceful, disreputable, double-dealing, double-faced, double-tongued, duplicitous, fallacious, false, fraudulent, furacious [archaic], honorableness [US], honorificabilitudinitatibus, honourableness [Brit, Cdn], ignoble, ignominious, inglorious, insincere, Janus-faced, misleading, opprobrious, picaresque, rascally, roguish, scoundrelly, shabby, shameful, thieving, thievish, two-faced, unjust, unprincipled, untrustworthy, untrusty, unworthy, yellow

Antonym: honorable [US], honourable [Brit, Cdn]