Attacked the copper with acid (6)
I believe the answer is:
etched
'acid' is the definition.
Both the definition and answer are adjectives. Maybe they are linked in a way I don't understand?
'attacked the copper' is the wordplay.
I cannot really understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
'copper' could be 'd' and 'd' is found in the answer.
The remaining letters 'eche' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'with' is the link.
Can you help me to learn more?
(Other definitions for etched that I've seen before include "Engraved, eg, by acid" , "made some kind of score" , "Carved on metal with acid" , "Incised" , "Cut or impressed into a surface" .)