A European loses the head in Paris, for instance, out of bitterness, in a manner of speaking (8)
I believe the answer is:
acerbity
'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" .)