The word "most unvirtuous" is a compound adjective that describes someone who lacks moral goodness or ethical behavior. The antonyms for this term would be the opposite of being unvirtuous or immoral. Therefore, the antonyms of "most unvirtuous" would be "most virtuous," which describes someone who is morally upright and ethical in their behavior. Other antonyms include "righteous," "noble," "upright," "honest," "integrity," "justice," and "reasonableness." Using these antonyms to describe someone would generally be a compliment, indicating that the person in question has high moral standards and acts in accordance with them.