Copper linked with exquisite poison (6)
I believe the answer is:
curare
'poison' is the definition.
(curare is a poisonous plant)
'copper linked with exquisite' is the wordplay.
'copper' becomes 'cu' (Cu is the chemical symbol for copper).
'linked with' is a charade indicator (letters next to each other).
'exquisite' becomes 'rare'.
'cu'+'rare'='CURARE'
(Other definitions for curare that I've seen before include "Paralysing plant poison" , "Arrow poison" , "Poison used on darts" , "Poison put on arrows" , "Poison applied to darts" .)