Cry of discovery (6)
I believe the answer is:
eureka
'cry of discovery' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for eureka that I've seen before include "Triumphant exclamation of discovery" , "I've got it!" , "Cry of joy on finding something" , "Discovery announcement" , "Exultant cry" .)