The Gershwin who composed an air (3)
I believe the answer is:
ira
'the gershwin who composed an' is the definition.
'ira' can be an answer for 'the gershwin' (ira gershwin is george gershwin's brother). I'm unsure of the rest of the definition.
'air' is the wordplay.
I cannot really see how this works, but
an anagram of 'air' is 'ira' which is present in the answer.
No letters remain.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for ira that I've seen before include "Brother of George Gershwin" , "George Gershwin's older brother, the lyricist" , "Gershwin, say" , "Songwriter George's elder brother" , "Militant Irish nationalist organisation" .)