Composer from Unterbergen (4)
I believe the answer is:
berg
'composer' is the definition.
(20th Century Austrian composer)
'from unterbergen' is the wordplay.
'from' indicates the answer is hidden within the clue.
'BERG' is hidden within 'unterbergen'.
(Other definitions for berg that I've seen before include "Mountain; Alban --, composer" , "One who scored" , "Possible shipping hazard" , "Alban -, composer (Wozzeck, Lulu)" , "Viennese composer" .)