US five-cent piece (6)
I believe the answer is:
nickel
'us five-cent piece' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for nickel that I've seen before include "US five cent piece" , "Metallic element; US coin" , "Five-cent piece in the US" , "Coin worth half a dime" , "American five cent piece" .)