Oppressive credo Nero used in part? (7)
I believe the answer is:
onerous
'oppressive' is the definition.
(I've seen this in another clue)
'credo nero used in part?' is the wordplay.
'in part?' indicates the answer is hidden within the clue (I've seen 'in part' mean this).
'ONEROUS' can be found hidden inside 'credo nero used'.
(Other definitions for onerous that I've seen before include "quite a burden if so" , "Burdensome, oppressive" , "Involving a great deal of effort" , "'Burdensome, not easily borne (7)'" , "Challenging" .)