A not-really-relevant aside: most philosophers don't own philosophical dictionaries, but let that pass.
Here's a non-philosophical word: unicorn. It's easy to explain what it means, but there aren't any real-life examples. Whether a term can be clearly explained and whether there are actual examples are quite different questions.
If it's controversial whether something exists then a philosopher shouldn't pretend otherwise, but the question of whether something exists (God, for instance) might be an interesting one. And sometimes the best way to understand a notion is a philosophical question. The notion of free will is like that. In that case, there's no one meaning for the term, but it's possible to have a perfectly reasonable discussion of what might count as free will and why some answers might be better than others. In fact that sort of discussion comes up in many disciplines. Philosophers are unusual in that they're trained to notice this kind of unclarity and to reason about it carefully.