I calm us with arrangement that's harmonious (7)

I believe the answer is:

musical

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

'harmonious' is the definition.
(thesaurus)

'i calm us with arrangement' is the wordplay.
'i calm us' anagrams to 'MUSICAL'.
Though, I am not sure how the anagram is indicated.

'that's' is the link.

Can you help me to learn more?

(Other definitions for musical that I've seen before include "Annie maybe" , "Annie or Mame, say" , "Stage show; harmonious" , "Show with singing and dancing" , "Eg, Les Miserables" .)

I've seen this clue in The Everyman puzzle in The Observer.

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