Explanation:

- Knave: A term often used to describe a dishonest or deceitful person.

- Option 1: Ornamental

- Doesn't fit as an antonym since it refers to something decorative and is unrelated to a person's character.

- Option 2: Dishonest

- This would be a synonym, not an antonym, as it also describes someone who lacks honesty.

- Option 3: Hero

- Hero is the correct antonym. A hero is often characterized by traits such as honesty and integrity, which are opposite to those of a knave.

- Option 4: Villain

- A villain, like a knave, also implies negative traits but on a larger scale, so it's closer to a synonym than an antonym.