Determined English union, unsuccessful one rising (8)
I believe the answer is:
resolute
'determined' is the definition.
(similar in meaning)
'english union unsuccessful one rising' is the wordplay.
'english' becomes 'e' (abbreviation).
'union' becomes 'tu' (abbreviation for trade union).
'unsuccessful one' becomes 'loser' (someone who failed to win).
'rising' shows that the letters should be reversed in order (going up in a down clue).
'e'+'tu'+'loser'='etuloser'
'etuloser' backwards is 'RESOLUTE'.
(Other definitions for resolute that I've seen before include "Reels out (anag.)" , "'Firm, unhesitating (8)'" , "Firm in purpose" , "'With fixed purpose, steadfast (8)'" , "Determined, unwavering" .)