The antonyms for the phrase "under hand" include "aboveboard," "forthright," and "straightforward." These words all suggest honesty, clarity, and openness. A person or action that is aboveboard is conducted in an open and honest manner. It is not secretive or sneaky. Something that is straightforward is direct, clear, and easy to understand. It is not confusing or misleading. And something that is forthright is honest, direct, and sincere. It is not deceitful or underhanded. When we use antonyms to describe actions or behaviors, we help others understand the difference between what is ethical and what is not.