The term "art aboveboard" refers to something that is fair, honest, and legitimate. Therefore, antonyms for this term would include words that signify dishonesty, deception, and underhandedness. Some antonyms of "art aboveboard" include words like shady, deceptive, disingenuous, fraudulent, corrupted, duplicitous, crafty, and cunning. These words depict that the opposite of being morally upright and sincere is to be deceitful and cunning. When one behaves in a manner that is not aboveboard, it can lead to negative consequences and harm others. It is essential to uphold the value of honesty and integrity in all aspects of life.