Last decider (5)
I believe the answer is:
final
I believe this is a double definition.
'last' is the first definition.
(synonyms)
'decider' is the second definition.
(eg decider in a sporting contest)
(Other definitions for final that I've seen before include "Coming at the end" , "Last in a series of games or contests" , "Not to be altered" , "big match" , "Last match in a competition" .)