Rat reversing English cutter (5)
I believe the answer is:
knife
'cutter' is the definition.
(I know that knife is a knife)
'rat reversing english' is the wordplay.
'rat' becomes 'fink' (fink is a kind of rat).
'reversing' is a reversal indicator.
'english' becomes 'E' (abbreviation).
'fink' back-to-front is 'knif'.
'knif'+'e'='KNIFE'
(Other definitions for knife that I've seen before include "Lethal weapon" , "Cutlery item" , "Eating utensil" , "Sharp tool" , "Piece of cutlery" .)