Arrogant mood, by the sound of it (4)

I believe the answer is:

vain

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'arrogant' is the definition.
(thesaurus)

I cannot understand how the rest of the clue works.

(Other definitions for vain that I've seen before include "Forever looking in the mirror" , "Useless; conceited" , "It's no good" , "Conceited - or a waste of time" , "Stuck-up? It's hopeless" .)

I've seen this clue in The Hindu.

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