Rail: Labour rejected American deal (10)
I believe the answer is:
balustrade
'rail' is the definition.
(balustrade is a kind of rail)
'labour rejected american deal' is the wordplay.
'labour' becomes 'lab'.
'rejected' is a reversal indicator.
'american' becomes 'us'.
'deal' becomes 'trade' ('trade' can be a synonym of 'deal'**).
'lab' written backwards gives 'bal'.
'bal'+'us'+'trade'='BALUSTRADE'
(Other definitions for balustrade that I've seen before include "Railing at the side of a balcony" , "Parapet" , "Row of pillars under rail" , "Row of short pillars with coping" , "Stair rail and its supports" .)