A Gershwin (3)
I believe the answer is:
ira
'a gershwin' is the definition.
(lyricist Ira Gershwin, brother of George)
This is the entire clue.
(Other definitions for ira that I've seen before include "Illegal organisation, in short" , "George Gershwin's older brother, the lyricist" , "Brother of George Gershwin" , "terrorists" , "Gershwin, say" .)