Go beyond former prison room briefly (5)
I believe the answer is:
excel
'go beyond' is the definition.
(thesaurus)
'former prison room briefly' is the wordplay.
'former' becomes 'ex'.
'prison room' becomes 'cell' (I've seen this before).
'briefly' means to remove the last letter.
'cell' with its final letter removed is 'cel'.
'ex'+'cel'='EXCEL'
(Other definitions for excel that I've seen before include "Do particularly well" , "cap" , "Eclipse" , "Outrival" , "Do better than, give great performance" .)