Do away with prison cell briefly (6)
I believe the answer is:
cancel
'do away with' is the definition.
(thesaurus)
'prison cell briefly' is the wordplay.
'prison' becomes 'can' (the can is American slang for prison**).
'briefly' means to remove the last letter.
'cell' with its last letter taken away is 'cel'.
'can'+'cel'='CANCEL'
(Other definitions for cancel that I've seen before include "Scrub" , "Cross out or abolish" , "Call off or invalidate" , "Strike out" , "stop?" .)