Pound piece (5)
I believe the answer is:
ounce
'pound piece' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ounce that I've seen before include "16 for a pound" , "Imperial unit of weight" , "A light imperial measure of weight" , "Approx. twenty-eight gm" , "There are quite a few in the pound" .)