Dictionary:

dishonorable

  (dĭs-ŏn'ər-ə-bəl)

1. Characterized by or causing dishonor or discredit.
2. Lacking integrity; unprincipled.

adjective

Meriting or causing shame or dishonor: discreditable, disgraceful, disreputable, ignominious, opprobrious, shameful. See respect/contempt/standing.

Definition: shameful, corrupt
Antonyms: blameless, ethical, honorable, principled, respectable, trustworthy, uncorrupt, worthy

The adjective has 5 meanings:

Meaning #1: lacking honor or integrity; deserving dishonor
  Synonym: dishonourable
  Antonym: honorable (meaning #2)

Meaning #2: deceptive or fraudulent; disposed to cheat or defraud or deceive
  Synonym: dishonest

Meaning #3: not bringing honor and glory
  Synonym: inglorious

Meaning #4: not adhering to ethical or moral principles
  Synonyms: base, dishonourable, immoral, unethical

Meaning #5: morally unacceptable
  Synonym: dishonourable