Initially fed up, joins in finding Japanese volcano (4)
I believe the answer is:
fuji
'japanese volcano' is the definition.
(I've seen this before)
'initially fed up joins in' is the wordplay.
'initially' says to take the initial letters.
The first letters of 'fed up joins in' is 'FUJI'.
'finding' acts as a link.
(Other definitions for fuji that I've seen before include "Extinct volcano is the highest peak in Japan" , "Extinct volcano in south central Honshu" , "Mount of Japan" , "Sacred Japanese peak" , "Japan's sacred mountain" .)