Elgar composition for portable organ (5)
I believe the answer is:
regal
'portable organ' is the definition.
(historical type of organ)
'elgar composition' is the wordplay.
'composition' is an anagram indicator.
'elgar' is an anagram of 'REGAL'.
'for' is the link.
(Other definitions for regal that I've seen before include "fit for the Queen" , "'Majestic, royal (5)'" , "Kingly or queenly" , "befitting a king" , "Kingly glare?" .)