Obtuse renegade, inwardly calm (6)

I believe the answer is:

serene

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'calm' is the definition.
(synonyms)

'obtuse renegade inwardly' is the wordplay.
'SERENE' is hidden in amongst the letters.
However, I am unsure how this is indicated.

Can you help me to learn more?

(Other definitions for serene that I've seen before include "Calm, untroubled" , "Not agitated" , "Calm, peaceful, tranquil" , "Calm and at peace" , "Placid" .)

I've seen this clue in The Mirror.

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