Mount ---, Japan’s highest peak (4)
I believe the answer is:
fuji
I believe this is a double definition.
'mount' is the first definition.
(I have seen 'Mount of Japan' mean 'fuji' so perhaps 'mount' could also mean 'fuji')
'japan's highest peak' is the second definition.
(I've seen this before)
(Other definitions for fuji that I've seen before include "Sacred volcano of Japan" , "Japan's highest peak" , "Highest Jap. mountain" , "Sacred Japanese mountain" , "Extinct volcano in central Japan" .)