I'm not sure why Tyson, Hawking, Krauss, Dawkins, Coyne, Feynman, et al., express so much contempt for philosophy. But my best guess is that they're ignorant -- unaware -- of what philosophy is when it's done well, perhaps because they received little or no academic training in philosophy when they were undergraduate students. (By the time they reached graduate school in the sciences, it may have been too late for them to get that training even if they had been interested in getting it.)
I don't think they're using different definitions, at least not systematically. Krauss does claim that physics has redefined the words "something" and "nothing," but I think he's deeply mistaken (see Question 4759). In general, I find that when non-philosophers, including scientists, reason about philosophical issues, they do so sloppily: making elementary mistakes in inference, conflating concepts that ought to be kept distinct, and so on. That's unfortunate but not surprising, since reasoning well about philosophical issues takes training: why shouldn't it? My sense is that their rigorous training was focused very narrowly on particular topics in physics or biology, and outside that narrow range they're no better reasoners than the average person -- and perhaps worse, because the deference they've been accorded as scientists has made them overconfident (hence insufficiently careful) about topics outside their specialties. Nor do I think that they're attacking just bad philosophy, because I'm not convinced that they can distinguish bad philosophy from good.