Compunction (noun)

1. A feeling of guilt or moral scruple that prevents or follows the doing of something bad.
2. Remorse for a past action or behavior.

Origin:

From latin compunctio, from compungere, meaning to prick.

Examples:

1. He felt a compunction for the way he had treated his friend.
2. She had no compunction about lying to her boss.
3. He felt a compunction for his past actions and decided to make amends.
4. The compunction was overwhelming and he couldn't shake it off.
5. He had no compunction about cheating on the test because he believed it was fair game.