College of punishment (3)
I believe the answer is:
uni
'college' is the definition.
(short for university)
'of punishment' is the wordplay.
'of' indicates the answer is hidden within the clue.
'UNI' is hidden in the letters of 'punishment'.
(Other definitions for uni that I've seen before include "College, colloquially" , "Seat of learning" , "academic establishment" , "Reading is one" , "Place of higher education (abbr)" .)