 It would be a mistake to take “cube” to be a natural kind term understood through some reference-fixing description such as: a three-dimensional solid that looks such-and-such a way when looked at from various angles and that feels so-and-so when turned around in your hands; is able to fit snugly through square holes cut out of a board, etc. “Cube” is not a natural kind term and we understand what a cube is through understanding its definition, namely, a three-dimensional solid with six faces all of which are squares.