We also have "gaseous" and "icy" for composition, "minor" (a.k.a. asteroids) and a relatively new adjective for planets: extrasolar.

I've been skimming Wikipedia's article, Defenition of planet, looking for clues. It's all semantics, of course... but as any biologist knows, nomenclature can have a huge importance, especially as the number of examples grows and diversifies.

One clue that's setting up sympathetic vibrations in me is the phrase "trans-Neptunian". That's kind of long-winded, so perhaps "Kuiperian" might be used instead. Call 'em all planets if they satisfy all three criteria: orbit the Sun, not another body; diameter > 2000 km; stable shape due to internal gravity.

Three adjectives would get the job done: major (the original 8); minor (the asteroids); Kuiperian (Pluto & Co.). Then Pluto gets to remain a planet, Charon gets to remain Pluto's moon, and we get to expand the list of named planets for star-struck kids to memorize and show off with (as I did when a pre-schooler).