At this moment briefly more strung out? Not any more! (8)
I believe the answer is:
nolonger
'not any more' is the definition.
(I've seen this before)
'at this moment briefly more strung out?' is the wordplay.
'at this moment' becomes 'now' (I've seen this in another clue).
'briefly' means to remove the last letter.
'more strung out?' becomes 'longer' (I've seen this in another clue).
'now' with its last letter taken away is 'no'.
'no'+'longer'='NOLONGER'
(Other definitions for nolonger that I've seen before include "Not now as formerly" , "Not now or in the future" , "Waist and stomach" , "That's gone on for enough time - make shorter or briefer" .)