Shifty copper caught up in nasty hole (6)
I believe the answer is:
louche
'shifty' is the definition.
(I've seen this before)
'copper caught up in nasty hole' is the wordplay.
'copper' becomes 'cu' (chemical symbol).
'caught up' says the letters should be written in reverse (in a down clue, letters go up).
'in' indicates putting letters inside.
'nasty' indicates anagramming the letters (a nasty or wrong spelling).
'cu' reversed gives 'uc'.
'hole' with letters rearranged gives 'lohe'.
'uc' going into 'lohe' is 'LOUCHE'.
(Other definitions for louche that I've seen before include "Shasy or questionable, from France" , "Questionable or shady, from French" , "Seedy" , "Ignominious" , "Appealingly disreputable" .)