Coming together every year in Greek capital (7)

I believe the answer is:

allying

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'coming together' is the definition.
Although both the answer and definition are present participle verbs, I cannot understand how they can define each other.

'every year in greek capital' is the wordplay.
'every' becomes 'all' (similar in meaning).
'year' becomes 'y'.
'capital' indicates taking the first letters.
The initial letter of 'greek' is 'g'.
'all'+'y'+'in'+'g'='ALLYING'

Can you help me to learn more?

(Other definitions for allying that I've seen before include "Making United" , "Getting together" , "Uniting for mutual benefit" , "Union" .)

I've seen this clue in the Sydney Morning Herald.

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