Good to deliver in box (4)
I believe the answer is:
grid
'box' is the definition.
(a grid is a square design)
'good to deliver' is the wordplay.
'good' becomes 'g' (abbreviation).
'to deliver' becomes 'rid' (e.g. deliver us from evil).
'g'+'rid'='GRID'
'in' is the link.
(Other definitions for grid that I've seen before include "Power distribution network" , "Electricity network" , "Electrical network - American football field - grating" , "Framework of crossing lines" , "Rectangular framework" .)