Dimension not initially given for cube (5)
I believe the answer is:
eight
'for cube' is the definition.
(8 is a cube number)
'dimension not initially' is the wordplay.
'dimension' becomes 'height' (height is a kind of dimension).
'not initially' means to remove the first letter.
'height' with its initial letter taken off is 'EIGHT'.
'given' is the link.
(Other definitions for eight that I've seen before include "Rowing boat crew" , "destroyed [IN 8A] here!" , "Figure" , "Number; rowing boat" , "team rowing" .)