Badly tempered copper put in current gold coin (7)
I believe the answer is:
iracund
'badly tempered' is the definition.
The answer and definition are different parts of speech. However, past participle verbs and adjectives can sometimes define each other.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for iracund that I've seen before include "Easily riled" , "Easily angered" , "tetchy" , "swiftly angered" .)