"Hurray!" (6)
I believe the answer is:
yippee
'hurray' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for yippee that I've seen before include "I'm deliriously happy!" , "Exclamation of wild delight (colloq.)" , "Excellent!" , "expression of celebration" , "Hurray" .)