Greatly multiply little bit of sugar (4)
I believe the answer is:
cube
I believe this clue is a double definition.
'greatly multiply' is the first definition.
(as in cubing a number)
'little bit of sugar' is the second definition.
(sugar cube)
(Other definitions for cube that I've seen before include "Die" , "Times itself twice" , "Regular three dimensional figure" , "Square-sided solid" , "8 possibly" .)