Someone ultimately wicked you may give a bad look (4,3)
I believe the answer is:
evil eye
'a bad look' is the definition.
(I've seen this in another clue)
'someone ultimately wicked you may' is the wordplay.
'ultimately' indicates one should take the final letters.
'wicked' becomes 'vile' (similar in meaning).
'you may' becomes 'ye' (I've seen this in other clues).
The final letter of 'someone' is 'e'.
'e'+'vile'+'ye'='EVIL EYE'
'give' acts as a link.
(Other definitions for evil eye that I've seen before include "Optical sort of ancient curse" , "Look that can be harmful?" , "Gaze or stare believed to cause harm" , "Malevolent look" , "Look that inflicts harm" .)