Stern characters won't participate in organised treasure hunt, showing proud haughtiness (7)

I believe the answer is:

hauteur

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'haughtiness' is the definition.
(I know that haughtiness can be written as hauteur)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for hauteur that I've seen before include "High-handedness" , "Disdainful pride or snobbery" , "Surquedy" , "Nose-in-the-air pride" , "Lofty pride, looking down on others" .)

I've seen this clue in The Irish Times.

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