Cut up, making many a nice mess (5)
I believe the answer is:
mince
'cut up' is the definition.
(I've seen this before)
'many a nice mess' is the wordplay.
'many' becomes 'm' (Roman numeral for a thousand).
'mess' indicates anagramming the letters.
'nice' anagrammed gives 'ince'.
'm'+'ince'='MINCE'
'making' acts as a link.
(Other definitions for mince that I've seen before include "Walk daintily" , "meat in small portions" , "Finely chopped meat" , "Finely cut meat" , "Dice" .)