Comedian's foil (6)
I believe the answer is:
stooge
'comedian's foil' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for stooge that I've seen before include "Butt of a comic's jokes" , "Comedian's assistant-victim" , "lackey" , "A comedian's assistant, butt of his jokes" , "comedy partner" .)