Geometric solid (4)
(Other definitions for cube that I've seen before include "Three-dimensional square" , "nine?" , "Geometrical solid" , "Three-dimensional shape with six sides" , "Square-faced solid" .)
'geometric solid' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for cone that I've seen before include "Geometrical shape" , "Dry fruit of many evergreen trees, say pine" , "Volcano peak" , "Ice-cream cornet" , "Roadworks marker" .)