Good-looker makes a copper knot (5)
I believe the answer is:
cutie
'good-looker' is the definition.
(I've seen this in another clue)
'a copper knot' is the wordplay.
'a copper' becomes 'cu' (Cu is the chemical symbol for copper).
'knot' becomes 'tie' (I've seen this before).
'cu'+'tie'='CUTIE'
'makes' acts as a link.
(Other definitions for cutie that I've seen before include "Smasher" , "Attractive person or animal" , "beauty" , "an attractive thing" , "Smart female" .)