Big character in eg Belfast? (7)

I believe the answer is:

capital

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'eg belfast?' is the definition.
(belfast is a kind of capital)

'big character' is the wordplay.
'big' becomes 'capita' (I can't justify this - if you can you should give a lot more credence to this answer).
'character' becomes 'l'.
'capita'+'l'='CAPITAL'

'in' is the link.

Can you help me to learn more?

(Other definitions for capital that I've seen before include "Block" , "Upper case city" , "Means" , "Money - chief city" , "A big letter, or a big city" .)

I've seen this clue in The Times.

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