Changeless good spirit (5)

I believe the answer is:

angel

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

'spirit' is the definition.

'changeless good' is the wordplay.
'ANGEL' is hidden within the letters.
But, I'm not sure how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for angel that I've seen before include "local to Islington" , "Theatre backer" , "Christmas tree decoration" , "One backing plays" , "Divine messenger" .)

I've seen this clue in the Evening Standard.

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