I am not trying to be difficult, but I am not sure philosophy is difficult to define, or at least I suggest it is not any more difficult to define than (for example) the sciences, the humanities, love or works of art, war and peace, and so on. I usually define "philosophy" as having two levels or dimensions. On the one had, and most generally, to have a view of reality and values is to have a philosophy. Given this general definition, every thoughtful person has a philosophy of some kind. Going further, it should be noted that philosophy involves critical reflection on one or more such views, inquiring into meaning and coherence and raising questions of justification (why accept one view rather than another? or why accept any view at all?) This definition (or maybe it should be thought of as a "characterization" or depiction or sketch) can then be enhanced by offering examples and then by noting how philosophy has a host of sub-fields from metaphysics, epistemology, ethical theory or, more broadly axiology, etc, and then by taking note of still further sub-fields such as the philosophy of science, philosophy of religion, philosophy of art, and so on.
Difficulties might emerge, however, insofar as defining philosophy in further detail most likely will have to involve the practice of philosophy. There are controversial philosophical views on the nature and methodologies that are promising in, say, metaphysics.
I must concede that some further difficulties could still emerge, notwithstanding my optimistic opening paragraph. An element of the definition of philosophy I have not mentioned so far is based on the etymology of "philosophy," which comes from the Greek for the love of wisdom. I am inclined to the view that goes back to Socrates and Plato that the life of a philosopher is one that involves (or should involve) practicing the love of wisdom. It is, therefore, a way of life. But there are some philosophers who prefer a more academic or theoretical (or abstracted?) approach to philosophy in which how you live (when you are not in the seminar room or conference) is beside the point. In the later case, someone may claim that one could be an outstanding philosopher (who, let us imagine, comes up with a brilliant philosophy of biology) but who lives a life of cruel indifference to the persons and values around him. In such a situation, perhaps I need to concede that defining "philosophy" is difficult, for I would say of the later (imagined) person that while he is "technically" doing outstanding philosophical work, he is not living his life in light of the love of wisdom and thus his claim to be a philosopher (in the full sense) is tainted.
So, in my reply, I offer a modest challenge to you by providing a (relatively) non-problematic (or not too messy) of a definition of philosophy, but then go on to concede that (interesting) difficulties can well emerge when one looks more closely at the details and boundaries of philosophy. My hope is that persons who grapple with defining philosophy might find themselves drawn into the practice of philosophy itself (a practice in light of my preferred definition) which will involve seeking to live out of the love of wisdom.