One of the Gershwins (3)
I believe the answer is:
ira
'one of the gershwins' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ira that I've seen before include "terrorists" , "nationalists" , "Brother of George Gershwin" , "Illegal organisation, in short" , "George 13 down's brother" .)