An element of law enforcement (6)
I believe the answer is:
copper
'an element' is the definition.
(copper is a kind of element)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for copper that I've seen before include "Atomic number 29" , "Police officer (slang)" , "Busy" , "An element; small coin" , "Metal - police officer" .)