Plain-dealing means being honest and straightforward in one's dealings. Some antonyms for plain-dealing are dishonesty, deception, trickery, and duplicity. Dishonesty refers to the lack of honesty or lying. Deception involves intentional misleading behavior to gain an advantage. Trickery involves the use of cunning and deceitful methods to achieve one's goals. Duplicity refers to the act of saying one thing and doing something else altogether. All these antonyms are associated with dishonesty and cannot be appreciated in any situation. Hence, it is essential to promote plain-dealing in all dealings to ensure transparency, trust, and ethical behavior.