Substantial cut in charity limits (5)
I believe the answer is:
chewy
'substantial' is the definition.
(chewy can mean substantial or hard)
'cut in charity limits' is the wordplay.
'cut' becomes 'hew' (hew can mean to chop or cut).
'in' is an insertion indicator.
'limits' means to remove the middle letters.
'charity' with its middle taken out is 'cy'.
'hew' going into 'cy' is 'CHEWY'.
(Other definitions for chewy that I've seen before include "Requiring mastication, like toffee say" , "Tough to masticate" , "Soft and sticky (to eat)" , "With a texture like toffee" , "Taking much mastication" .)