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In which a composer jots down his ideas? (8)

Ross

I believe the answer is:

notebook

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'in which a composer jots down his ideas?' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

This is the entire clue.

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(Other definitions for notebook that I've seen before include "Token boo as in pocket recorder with blank pages (8)" , "Jotter's accessory?" , "Bigger than diary, smaller than laptop" , "little computer" , "Small volume for brief records" .)

I've seen this clue in the Evening Standard.
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