Copper, extremely suspicious and stubborn sort (4)
I believe the answer is:
cuss
'stubborn sort' is the definition.
(I've seen this in another clue)
'copper extremely suspicious' is the wordplay.
'copper' becomes 'cu' (Cu is the chemical symbol for copper).
'extremely' says to hollow out the word (remove centre letters) (only the extremes of the word are used).
'suspicious' with its middle removed is 'ss'.
'cu'+'ss'='CUSS'
'and' is the link.
(Other definitions for cuss that I've seen before include "Blaspheme" , "Swear (slang)" , "Oath; (annoying sort of) person" , "Stubborn person" , "Use bad language (informal)" .)