Prison sentence for the enemy? (4)
I believe the answer is:
time
I believe this is a double definition.
'prison sentence' is the first definition.
(I've seen this before)
'the enemy?' is the second definition.
(the enemy when speaking figuratively)
'for' acts as a link.
(Other definitions for time that I've seen before include "Measure of duration" , "Duration; tempo" , "Indefinite period" , "It's measured by watch or clock" , "Age" .)