Audacious dean hums a terrible composition (9)

I believe the answer is:

unashamed

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'audacious' is the definition.
(similar in meaning)

'dean hums a terrible composition' is the wordplay.
'dean hums a' anagrams to 'UNASHAMED'.
Though, I am not clear how this is indicated.

Can you help me to learn more?

(Other definitions for unashamed that I've seen before include "not apologetic" , "Brazen" , "lacking any feeling of guilt" , "Without guilt or embarrassment" , "Showing no embarrassment" .)

I've seen this clue in The Irish Times.

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