Yes, cube is a Scrabble word!

Verb

1. Raise to the third power

2. Cut into cubes

Noun

1. A hexahedron with six equal squares as faces

2. A three-dimensional shape with six square or rectangular sides

3. The product of three equal terms

4. Any of several tropical American woody plants of the genus Lonchocarpus whose roots are used locally as a fish poison and commercially as a source of rotenone

5. A block in the (approximate) shape of a cube