Flatter at a duel (7)

I believe the answer is:

adulate

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'flatter' is the definition.
(adulating is a kind of flattering)

'at a duel' is the wordplay.
'at a duel' anagrams to 'ADULATE'.
However, I'm not clear how this is indicated.

Can you help me to learn more?

(Other definitions for adulate that I've seen before include "Flatter obsequiously" , "Worship" , "Praise obsequiously" , "Flatter excessively" , "Praise excessively" .)

I've seen this clue in The Irish News.

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