Mountain; composer (4)
I believe the answer is:
berg
I believe this clue is a double definition.
'mountain' is the first definition.
(I've seen this before)
'composer' is the second definition.
(20th Century Austrian composer)
(Other definitions for berg that I've seen before include "Lump of ice" , "South African mountain - Austrian composer" , "famously cut short a transatlantic journey" , "Large mass of floating ice" , "Mountain; shipping hazard" .)