Well, any classification system of anything will have some blurry spots around the edges, with objects that are sort of in one category and sort of in another, but the three I mentioned are pretty distinct, as such things go. Mercury, Venus, Earth, Luna, Mars, and Ceres are unambiguously rockballs; Jupiter, Saturn, Uranus, and Neptune are unambiguously gasballs; and Eris, Pluto, Sedna, Quaoar and the major moons of the gasballs are unambiguously iceballs. Just saying “fluid” or “solid” isn’t much help, because the subsurface oceans of Europa are very different from the molten core of the Earth, and you’d have to decide which layers count as “inside” and “outside” (is the Earth a solid crust under a fluid atmosphere, or a fluid outer core under a solid crust, or a solid inner core under a solid crust?).
Here’s a good one:
Cosmetics: From the idea that the universe (the cosmos) is perfection.
Don’t forget “star-crossed,” as in lovers like Romeo & Juliet.