Some villain's not well (3)
I believe the answer is:
ill
'not well' is the definition.
('ill' is the opposite to 'well')
'some villain's' is the wordplay.
'some' indicates the answer is hidden within the clue (some parts of the word are used).
'ILL' is hidden in the letters of 'villains'.
(Other definitions for ill that I've seen before include "Wicked" , "state, briefly" , "Sickly" , "Indisposed" , "Afflicted" .)