Ultimately, holiness affected devil (5)
I believe the answer is:
scamp
'devil' is the definition.
(I've seen this in another clue)
'ultimately holiness affected' is the wordplay.
'ultimately' says to take the final letters.
'affected' becomes 'camp' (camp can mean exaggerated or affected).
The last letter of 'holiness' is 's'.
's'+'camp'='SCAMP'
(Other definitions for scamp that I've seen before include "little monkey" , "Scallywag" , "Rogue - perform inadequately" , "Scoundrel" , "villain" .)