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A European loses the head in Paris, for instance, out of bitterness, in a manner of speaking (8)

Ross

I believe the answer is:

acerbity

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'manner of speaking' is the definition.
The answer and definition can be both human attributes as well as being singular nouns.
Maybe there's an association between them I don't understand?

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

Can you help me to learn more?

(Other definitions for acerbity that I've seen before include "roughness" , "Acrimony, bitterness" , "Sharp/forthright manner" , "Bitterness, sharpness" , "Sharpness, forthrightness" .)

I've seen this clue in the Irish Times (Crosaire) and The Irish Times.
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