Geometric figure (4)
(Other definitions for cube that I've seen before include "nine?" , "Square-faced solid" , "Shape made of six equal squares" , "Raise to the third power" , "product of three factors" .)
'geometric figure' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for cone that I've seen before include "Figure (for traffic control?)" , "Volcano peak" , "Edible ice cream container" , "16 Cornet" , "Hollow object associated with ice cream and motorways" .)
(Other definitions for octagon that I've seen before include "Eight-sided object" , "Figure with 8 sides" , "with eight angles" , "Eight-sided room" , "plane figure" .)