Wrongun is a British slang term used to describe someone who is dishonest or untrustworthy. It is a colloquialism that is often used in a light-hearted way. There are several synonyms for the word "wrongun" that can be used depending on the context. These include terms such as rogue, scoundrel, and rascal. Other synonyms for wrongun include cheat, fraudster, or con artist. These words all convey the idea of someone who is behaving in a deceitful or dishonest manner. Using these synonymns in place of wrongun can help to add variation to your vocabulary and make your language use more expressive.