Not well drilled in part (3)
I believe the answer is:
ill
'not well' is the definition.
('ill' is the opposite to 'well')
'drilled in part' is the wordplay.
'in part' says the answer is hidden in the clue.
'ILL' can be found hidden inside 'drilled'.
(Other definitions for ill that I've seen before include "Dicky" , "Evil or sick" , "Seasick" , "Not in the pink" , "laid up?" .)