I've found the answer! (6)
I believe the answer is:
eureka
(Other definitions for eureka that I've seen before include "Discoverer's triumphant cry" , "Cry announcing a brilliant discovery" , "announced by Archimedes" , "Archimedes' shout of triumph - re a uke (anag)" , "Archimedes' cry of triumph as he ran naked through the streets of Syracuse?" .)