The word "un tenable" could be described with a range of antonyms, or opposites, depending on the context in which it is being used. Some possible antonyms include sustainable, tenable, feasible, acceptable, logical, practical, reasonable, viable, and justifiable. These words suggest the opposite of something that is un tenable, or impossible to support, maintain, or defend. For example, if an argument is un tenable, then its antonym might be a logical or justifiable position. Similarly, if a project is un tenable, then its antonym might be a practical or feasible initiative. Regardless of the specific antonyms used, they all point towards a more positive, workable, and reasonable alternative.