Japan is said to move smartly ahead (6)
I believe the answer is:
nippon
'japan' is the definition.
(synonyms)
'said to move smartly ahead' is the wordplay.
I cannot really understand how this works, but
'ahead' could be 'on' (synonyms) and 'on' is located in the answer.
This may be the basis of clue (or it may be nonsense).
'is' acts as a link.
Can you help me to learn more?
(Other definitions for nippon that I've seen before include "Transliteration of "Japan"" , "Japanese name for Japan (6)" .)