It's not right that our Gallic friends are swollen headed (5)

I believe the answer is:

amiss

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'it's not right' is the definition.
(I've seen this in another clue)

I don't understand how the rest of the clue works.

(Other definitions for amiss that I've seen before include "astray" , "Wrong - awry" , "In an inappropriate way" , "Out of order" , "Fallacious" .)

I've seen this clue in the Evening Standard.

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