No, this might have been the first time you encountered this word. It is the Duolingo way of teaching. We are expected to do our best and if we make a mistake Duolingo tells us that. Then it is up to us to solve this problem, by looking it up somewhere or look here at the discussion. If we still don't get a satisfactory explanation, we might ask what is going on and then some fellow student might be able to help. Then we repeat the lesson until we know it well enough.