Triumphant cry (6)
I believe the answer is:
eureka
'triumphant cry' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for eureka that I've seen before include "Cry announcing a brilliant discovery" , "Exclamation of triumph" , "Exclamation of triump from Archimedes" , "Archimedes' cry of triumph as he ran naked through the streets of Syracuse?" , "Exclamation of discovery by Archimedes" .)