The sort of definition that philosophers are interested in, insofar as they are interested in definitions at all, is one that identifies the intension , not the extension of the word. An excellent definition of the word 'bachelor' is 'unmarried man'. Aside from being practically impossible, such a list is just not what we are looking for. After all, what we are interested in is a description of what all those things we call 'bachelors' have in common, which distinguishes them from all non-bachelors. Notice now that there are two different ways in which the meanings of words can be unclear .
Most words are, in fact, both ambiguous and vague.
So certainly, a word that is both ambiguous and vague can have a rich fund of meaning. The meaning of 'definition' With this background, it will be easier to discuss definitions. Suppose we have decided on some word, or concept associated with the word, to define. Suppose also that we have identified which sense of the word we are interested in, and we have noted clear cases, some unclear cases, and some borderline cases of the application of the word. Even if those philosophers are right, they will, most of them, still acknowledge that in philosophy we should do something like give definitions of important philosophical concepts.