In Japan, the only circular temple (8)
I believe the answer is:
pantheon
'temple' is the definition.
(a pantheon is a temple for multiple gods)
'in japan the only circular' is the wordplay.
'in' indicates a hidden word.
'PANTHEON' is hidden in the letters of 'japan the only circular'.
(Other definitions for pantheon that I've seen before include "building that was built to honour gods" , "Group of greats" , "Hall of fame" , "Temple of all the gods in ancient Greece" , "church" .)