Remain outside a silent old prison (8)
I believe the answer is:
bastille
'old prison' is the definition.
(historical French prison)
'remain outside a silent' is the wordplay.
'remain' becomes 'be' (eg be patient, remain patient).
'outside' indicates putting letters inside.
'silent' becomes 'still' (synonyms).
'a'+'still'='astill'
'be' placed around 'astill' is 'BASTILLE'.
(Other definitions for bastille that I've seen before include "Parisian fortress" , "Paris prison, now opera" , "Old Parisian prison" , "French jail" , "Paris prison stormed in 1789 ad." .)