Boredom featured by unseen nuisance (5)

I believe the answer is:

ennui

I'm a little stuck... Click here to teach me more about this clue!

'boredom' is the definition.
(I know that boredom can be written as ennui)

'featured by unseen nuisance' is the wordplay.
'ENNUI' is hidden within the letters.
However, I am unsure how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for ennui that I've seen before include "Boredom, dullness" , "French boredom and lassitude" , "Listless feeling" , "depression" , "to make one list less when connected" .)

I've seen this clue in the Sydney Morning Herald.

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