Select the most appropriate ANTONYM of the given word.
Upright

The correct answer is Immoral.

Explanation:
An antonym is a word that has the opposite meaning of a given word.
The given word is "Upright". In a moral context, "upright" means behaving in a moral, honest, and honorable way (having high ethical standards).
Let us analyze the meanings of all the given options to find the opposite:

1. Stout: Having a thick, strong, or solid body; brave or determined. This is unrelated to the moral meaning of upright.
2. Immoral: Not conforming to accepted standards of morality; morally wrong or bad. This is the direct opposite of behaving in an honest and honorable (upright) manner.
3. Brave: Showing courage or ready to face danger. This is not the antonym of upright.
4. Ethical: Relating to moral principles; morally correct. This is a synonym of upright, not an antonym.

Therefore, Immoral is the most appropriate antonym of Upright.