Interestingly, the four traditional states of matter map very neatly (well, nearly so) to the
four ancient and medieval elements.
The last is a bit of a stretch, as "fire" usually refers to the process of oxidation, or a gas whose molecules are all in an excited energy state. However, the ancients also considered the Sun to be a ball of fire, and I bet if you showed a medieval alchemist an example of a plasma, he would probably have considered it "fire". Oh, and ionization is about as excited an energy state as you can get.