Pariah alone playing stringed instrument (7,4)
I believe the answer is:
aeolian harp
'stringed instrument' is the definition.
(aeolian harp is a kind of stringed instrument)
'pariah alone playing' is the wordplay.
'playing' indicates anagramming the letters.
'pariah'+'alone'='pariahalone'
'pariahalone' anagrammed gives 'AEOLIAN HARP'.
(Other definitions for aeolian harp that I've seen before include "Wind-operated instrument" , "It's played by the wind" , "Wind-played instrument" , "musical instrument" , "Wind-controlled instrument" .)