Greatest final (8)
I believe the answer is:
ultimate
This clue is a double definition.
'greatest' is the first definition.
(thesaurus)
'final' is the second definition.
(similar in meaning)
(Other definitions for ultimate that I've seen before include "Final; fundamental" , "Last or highest" , "Last or concluding element" , "Conclusive" , "Utmost or extreme" .)