[firebrand]

Or change the definition of the word “planet.”

[Raymann]

They did in '06

A celestial body that is (a) in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

Pluto fails on the last point because of Charon, Nix, and Hydra.