Geographical location of Tammany Hall (5)

I believe the answer is:

amman

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'geographical location' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.

'of tammany hall' is the wordplay.
'of' indicates a hidden word.
'AMMAN' is hidden within 'tammany hall'.

Can you help me to learn more?

(Other definitions for amman that I've seen before include "A capital f-fellow in Jordan?" , "Jordanian city" , "Jordan's capital" , "Jordanian capital" , "City of Jordan" .)

I've seen this clue in the Evening Standard.

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