Moral philosophy is also philosophy, and it's only tangentially related to the structure of knowledge.

I think the problem with defining "philoosphy" is that any time a field becomes sufficiently well-defined, they stop calling it "philosophy". Natural philosophy is now "science". Early practitioners of economics, linguistics, and even law were called "philosophers". Fields like sociology and cognitive science still overlap a lot with philosophy departments.

What's left in philosophy is those fields that are still vague and without definitive answers even at the base level. Epistemology (structure of knowledge) and ethics are two broad headlines that encompass much of what's called "philosophy" now, but a lot of work in philosophy departments only barely fits into those categories (like those that also lump under sociology).

These fields are important, though it's easy for fans of "hard sciences" to dismiss them because they're so poorly defined. It's worth remembering that Newton and Darwin both considered themselves philosophers. They were the ones who took poorly defined fields to gave them rigorous footings, and we respect them for finding the order in what was orderless before they started.