Keen perception - having last word about copper? (6)
I believe the answer is:
acumen
'keen perception' is the definition.
(I've seen this before)
'last word about copper?' is the wordplay.
'last word' becomes 'amen' (last word in a prayer).
'about' indicates putting letters inside.
'copper?' becomes 'cu' (Cu is the chemical symbol for copper).
'amen' placed around 'cu' is 'ACUMEN'.
'having' acts as a link.
(Other definitions for acumen that I've seen before include "Mental keenness" , "Being sharp" , "Sharpness, penetration, quickness of perception" , "Gumption" , "Shrewdness, good for business" .)