Subway synonymous with Greek city - the state capital perhaps (10)
I believe the answer is:
metropolis
'greek city the state capital perhaps' is the definition.
I can't judge whether this definition defines the answer.
'subway synonymous' is the wordplay.
'subway' becomes 'metro' ('metro' can be a synonym of 'subway').
'synonymous' becomes 'polis' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'metro'+'polis'='METROPOLIS'
'with' is the link.
Can you help me to learn more?
(Other definitions for metropolis that I've seen before include "centre of activity" , "Major city of region" , "early film" , "Very large city" , "capital" .)