If an idea, an argument, a belief, or a position is tenable, you can hold on to it — you can keep defending it when other people push back, because the reasons behind it still stand up. It is a formal word, and it belongs to serious talk: academic writing, law, politics, editorials, a doctor explaining why one explanation of your symptoms fits and another does not. Here is the thing that surprises students: the negative is far more common than the positive. You will meet 'no longer tenable' and 'not tenable' many, many times for every one time you meet a plain 'that view is tenable'. People reach for this word most often at the moment a position collapses — 'after the new evidence, his story was simply not tenable.' So the natural home of the word is the sentence where something falls apart. Notice also that tenable is a modest kind of praise. It does not say an idea is right, or proved, or best. It says only that the idea survives — it has not been knocked down. A judge can say two opposite readings of a law are both tenable. So if you tell your professor 'your argument is tenable', do not expect a big smile; you have said it is defensible, not that it is good. There is a second, quite different use in British English that a dictionary will list separately: a job, a scholarship, or a position is 'tenable' for a period of time or at a place — 'the fellowship is tenable for three years, tenable at any UK university.' That means it can be held for that long, or held there. You will meet this one in scholarship applications, so it is worth knowing even though it sounds odd the first time.