A brilliant stroke allowed in poetry (7)
I believe the answer is:
couplet
'in poetry' is the definition.
(I know that couplet is part of poetry)
'a brilliant stroke allowed' is the wordplay.
'a brilliant stroke' becomes 'coup' (I've seen this in another clue).
'allowed' becomes 'let' (to let is to allow or permit).
'coup'+'let'='COUPLET'
(Other definitions for couplet that I've seen before include "Two lines of verse, often rhyming" , "piece of poetry" , "Pair of lines in poetry" , "bit of poetry" , "Pair of verse lines" .)