Nominally a horn composition (5)

I believe the answer is:

norah

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'nominally a horn composition' is the definition.
I can't tell whether this definition defines the answer.

'a horn composition' is the wordplay.
'composition' is an anagram indicator.
'a'+'horn'='ahorn'
'ahorn' with letters rearranged gives 'NORAH'.

Can you help me to learn more?

(Other definitions for norah that I've seen before include "Batty woman" , "Girl" , "Girl's name" .)

I've seen this clue in the Evening Standard.

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