Answer concerning a deed (5)
I believe the answer is:
react
'answer' is the definition.
(thesaurus)
'concerning a deed' is the wordplay.
'concerning' becomes 're'.
'a deed' becomes 'act' (I've seen this before).
're'+'act'='REACT'
(Other definitions for react that I've seen before include "Respond to a stimulus" , "Take" , "Retaliate" , "Acknowledge" , "What a chemical might do" .)