Grind carbon in the colliery (5)
I believe the answer is:
mince
'grind' is the definition.
(thesaurus)
'carbon in the colliery' is the wordplay.
'carbon' becomes 'C' (C is the chemical symbol for carbon).
'in the' means one lot of letters goes inside another.
'colliery' becomes 'mine' (a colliery is a coal mine).
'c' inserted into 'mine' is 'MINCE'.
(Other definitions for mince that I've seen before include "Chop food into small bits" , "Chop into tiny pieces" , "Cut fine" , "Grind (food)" , "Diced meat" .)