Glass of public radio (3)
I believe the answer is:
ira
'glass of public radio' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ira that I've seen before include "George 13 down's brother" , "nationalists" , "Brother of George Gershwin" , "Songwriter George's elder brother" , "George Gershwin's older brother, the lyricist" .)