The word means too many different things. And nobody really cares about the nature of matter, which they think they know pretty well from daily life, but on the nature of mind and spirit.
Reductionist – mind can be explained by material forces
Eliminativist – mind (or at least most theories of mind) are based on illusions and should not be taken seriously.
Economic vs. metaphysical
Naturalism (or anti-supernaturalism)
My theory which is mine
The material basis of mind is crushingly obvious. But the immaterial aspects of mind are perfectly real and either are reducible to material explanations or are at least implemented as mechanisms.
Whether the material or the immaterial is more foundational is a bogus non-question, which should be dissolved through nondualim or just by common sense.
I can't quite articulate the argument, but if you think about this long enough it starts to seems like a status game masquerading as philosophy. What's more important, ideas or mechanisms? It reduces down to a class conflict between people who are good at different forms of thought, but reality doesn't much care about that. See Omniorthogonal: A Consumer's Guide to the Foundations of Reality