Really upset contingent of Mykonos revellers (4,2)

I believe the answer is:

ever so

I'm a little stuck... Click here to teach me more about this clue!

'really' is the definition.
(I've seen this in another clue)

'upset contingent of mykonos revellers' is the wordplay.
'EVER SO' is hidden backwards within the letters.
But, I'm not sure how this is indicated.

Can you help me to learn more?

(Other definitions for ever so that I've seen before include "Greatly" , "Intensifier" , "Very much" , "To a very great extent" , "Extremely" .)

I've seen this clue in The Independent.

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