Formal wear kept nice butcher powerless (7)
I believe the answer is:
necktie
'formal wear' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for necktie that I've seen before include "one from the old school?" , "this'll go with shirt" , "Long narrow piece of material worn knotted at the front" , "Material worn knotted round throat" , "Band in the US" .)