Cutter's back at last with nickel and iron (5)
I believe the answer is:
knife
'cutter's' is the definition.
(knife is a kind of cutter)
'back at last with nickel and iron' is the wordplay.
'at last' says to take the final letters.
'with' means one lot of letters go next to another.
'nickel' becomes 'ni' (Ni is the chemical symbol for nickel).
'and' is a charade indicator (letters next to each other).
'iron' becomes 'fe' (Fe is the chemical symbol for iron).
The last letter of 'back' is 'k'.
'k'+'ni'+'fe'='KNIFE'
(Other definitions for knife that I've seen before include "Cutlery item" , "Dagger" , "Cutting tool" , "Cutter" , "Cutting blade" .)