Nominally a horn composition (5)

I believe the answer is:

norah

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

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

'a horn composition' is the wordplay.
'composition' indicates anagramming the letters (letters arranged or composed in a different order).
'a'+'horn'='ahorn'
'ahorn' is an anagram of '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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