Labour shadow clinches a victory (7)
I believe the answer is:
travail
'labour' is the definition.
(I know that labour can be written as travail)
'shadow clinches a victory' is the wordplay.
'shadow' becomes 'trail' (trailing is a kind of shadowing).
'clinches' is an insertion indicator (inserted letters are embraced or clinched).
'victory' becomes 'v'.
'a'+'v'='av'
'trail' enclosing 'av' is 'TRAVAIL'.
(Other definitions for travail that I've seen before include "Exertion, elbow grease" , "Toil - anguish" , "Old word for pangs of childbirth" , "painful exercise" , "Painful or laborious effort, like childbirth" .)