Very large, also known as great city in Japan (5)
I believe the answer is:
osaka
'city in japan' is the definition.
(I've seen this in another clue)
'very large also known as' is the wordplay.
'very large' becomes 'os' (abbreviation for oversize).
'also known as' becomes 'a.k.a.' (synonyms).
'os'+'aka'='OSAKA'
'great' acts as a link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for osaka that I've seen before include "Major port and commercial and industrial centre on Honshu" , "Kinki's capital" , "in east Asia" , "Japanese port city" , "Japanese port, Bay" .)