The word "un-tenable" means something that is difficult or impossible to defend or maintain. Antonyms of "un-tenable" include words like sustainable, viable, feasible, justifiable, and defensible. These words suggest something that is able to be supported, justified, or maintained over time. The word "sustainable" means something that is able to be maintained at a certain level without causing harm to the environment, society, or economy. The word "viable" suggests that something is capable of working, functioning, or surviving. The word "feasible" suggests that something is possible, practical or achievable. The words "justifiable" and "defensible" suggest that something is able to be supported, explained, or justified through reason and evidence.