Defining terms may seem dull and unnecessary, and most of the time it is - we don't have to define every term we use (that would be mad...) - but to simply and quickly define the term under discussion can save a lot of misunderstandings and frustration.
Having an interest in mathematics, I don't think defining terms is dull or unnecessary. To construct any kind of formal argument, it's imperative to define anything that isn't axiomatic, or doesn't have a widely accepted conventional definition.
That's not to say every definition should be hard and fast. I think dictionaries are supposed to describe the conventional use for a word, not proscribe a definition to it. I'm with Funt block in that the dictionary definition is sufficient, and diverging too far from its descriptive definitions put you into proscriptive territory. Ideally we'd all have expansive vocabularies that would allow us to use words with the perfect descriptions of the ideas we're trying to convey.
I'm not big on epistemology, I think it encourages talking around a subject rather than exploring it. But if there was ever a thread to get into one of the pillars of philosophy, I suppose this is it.