Deceive prisoner (3)
I believe the answer is:
con
This clue is a double definition.
'deceive' is the first definition.
(I've seen this before)
'prisoner' is the second definition.
(abbreviation for 'convict')
(Other definitions for con that I've seen before include "Deceive; prisoner" , "Learn; swindle" , "Dupe" , "Trick, deceive" , "Prisoner (sl.)" .)