Sequin half gleams under bridge (7)
I believe the answer is:
spangle
'sequin' is the definition.
('spangle' can be a synonym of 'sequin')
'half gleams under bridge' is the wordplay.
'half' indicates taking half.
'under' says to put letters next to each other.
'bridge' becomes 'span' ('span' can be a synonym of 'bridge'**).
'gleams' halved is 'gle'.
'gle' after 'span' is 'SPANGLE'.
(Other definitions for spangle that I've seen before include "it glitters" , "glitter" , "Glittery item" , "Glittering ornament" , "Needing bit of decoration" .)