Fifty retained by firm before certain shutdown (7)
I believe the answer is:
closure
'shutdown' is the definition.
(synonyms)
'fifty retained by firm before certain' is the wordplay.
'fifty' becomes 'L' (Roman numeral).
'retained by' indicates putting letters inside.
'firm' becomes 'co' (a firm is a company).
'before' is a charade indicator (letters next to each other).
'certain' becomes 'sure' (synonyms).
'l' put within 'co' is 'clo'.
'clo'+'sure'='CLOSURE'
(Other definitions for closure that I've seen before include "Stoppage" , "Resolution of emotional upheaval" , "Lose cur (anag.)" , "Feeling of emotional resolution" , "End; fastening" .)