Prisoner's room (4)
I believe the answer is:
cell
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">prisoner's room</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for cell that I've seen before include "Animal or plant building unit" , "Chamber" , "Place of incarceration in body unit" , "Biological unit with a nucleus" , "Part of a battery" .)