The girl I'm giving back the book to (6)

I believe the answer is:

missal

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'back the book to' is the definition.
I can't tell whether this defines the answer.

'the girl i'm' is the wordplay.
'the girl' becomes 'miss' (term of address for an unmarried woman).
'i'm' becomes 'al' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'miss'+'al'='MISSAL'

'giving' acts as a link.

Can you help me to learn more?

(Other definitions for missal that I've seen before include "Church book covering all services in the year" , "Service-book" , "Prayer-book" , "Book of prayers and rites" , "Book used at Catholic mass" .)

I've seen this clue in the Evening Standard.

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