Devious, but simply not devilish? (3)
I believe the answer is:
sly
'devious' is the definition.
(I've seen this before)
'simply not devilish?' is the wordplay.
'not' is a deletion indicator.
'devilish?' becomes 'imp' (I've seen this in other clues).
'simply' with 'imp' removed is 'SLY'.
'but' is the link.
(Other definitions for sly that I've seen before include "'Cunning, wily (3)'" , "Devious and furtive" , "Unpleasantly cunning and secretive" , "Cunning, foxy" , "Devious, cunning" .)