Imprisons many for a long time (5)
I believe the answer is:
cages
'imprisons' is the definition.
(I've seen this in another clue)
'many for a long time' is the wordplay.
'many' becomes 'c' (C is the Roman numeral for 100).
'for' is a charade indicator (letters next to each other).
'a long time' becomes 'ages' (ages can mean a very long time).
'c'+'ages'='CAGES'
(Other definitions for cages that I've seen before include "Locks up" , "Enclosures for animals" , "Wild animal enclosures" , "Enclosures made or wire or metal bars" , "prisons" .)