George Gershwin's brother (3)
I believe the answer is:
ira
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">george gershwin's brother</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ira that I've seen before include "Illegal organisation, initially" , "Gershwin, say" , "Militant Irish nationalist organisation" , "nationalists" , "Songwriter George's elder brother" .)