A US coin worth five cents (6)
I believe the answer is:
nickel
'a us coin worth five cents' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for nickel that I've seen before include "Element; five cents in US" , "An American 5-cent coin" , "One twentieth of a US dollar" , "Metal - 5 cents" , "Silvery-white metal" .)