Devil appearing in heaven is revealing (6)
I believe the answer is:
skimpy
'is revealing' is the definition.
(I've seen this before)
'devil appearing in heaven' is the wordplay.
'devil' becomes 'imp' (devilish creature).
'appearing in' means one lot of letters goes inside another.
'heaven' becomes 'sky' (I've seen this in another clue).
'imp' placed within 'sky' is 'SKIMPY'.
(Other definitions for skimpy that I've seen before include "Having hardly enough" , "Containing little excess" , "Meagre; (of clothes) short and revealing" , ", naughty thing, the blue skirts?" , "'Scanty, barely enough (6)'" .)