topic, count, material, substance, thing, weigh, affair, subject, issue, fact, more...

immaterial, insignificant, trivial, negligible, inconsequential

plasma, gas, liquid, solid, dark matter, more...

subject, organic, whole, simple, easy, white, different, important, gray, serious, difficult

mean a lot,   to be important,   solid object,   it is important to,   issue at hand,   physical things,   some solids,   be important,   physical reality,   be relevant