Anti study (3)
I believe the answer is:
con
I believe this clue is a double definition.
'anti' is the first definition.
(I've seen this in another clue)
'study' is the second definition.
(con can informally mean to study)
(Other definitions for con that I've seen before include "Dupe" , "This man is a swindler" , "one in pen?" , "Prisoner (sl.)" , "Study; steer" .)