Selection of Sen voicing a brief postscript (5)
I believe the answer is:
envoi
'postscript' is the definition.
(I have seen 'Poetic postscript' mean 'envoi' so perhaps 'postscript' could also mean 'envoi')
'selection of sen voicing a brief' is the wordplay.
'selection of' says the answer is hidden in the clue.
'ENVOI' can be found hidden inside 'sen voicing brief'.
(Other definitions for envoi that I've seen before include "Concluding words" , "Final stanza in ballad" , "Poetic conclusion to book" , "Concluding lines" , "Short stanza at end of ballade" .)