The phrase "most unwarrantable" pertains to a situation or action that is not justified, authorized, or allowed by law or treaty. Antonyms for this word include justified, legal, warranted, authorized, lawful, valid, permitted, and acceptable. An act can be deemed "justified" if it is morally right or in accordance with a valid reason. "Legal" means that something is permitted by law or enforced by the authorities. "Warranted" refers to a situation where something is supported by evidence or reason. "Authorized" implies that something has been approved or permitted by the person or party who has the power to do so. All these antonyms stand as legitimate and permissible actions, unlike "most unwarrantable.