There are a number of synonyms for the word "dishonourable" that can be used to describe a person, action or behaviour that lacks integrity or moral principles. Some of the most common synonyms include disreputable, disgraceful, immoral, unethical, corrupt, ignoble, shady, unprincipled, unscrupulous, fraudulent, and dishonest. These words can be used to describe a wide range of actions and behaviours, from lying and cheating to stealing and betraying trust. Whether used to describe an individual person or a larger system or organization, these synonyms all suggest a lack of honour and respect for others, and a disregard for the principles of honesty and fairness.