Book revealing the meaning of life? (10)

I believe the answer is:

dictionary

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'book' is the definition.
(I know that dictionary is a type of book)

I don't understand the rest of the clue.

(Other definitions for dictionary that I've seen before include "Ordered book" , "reference work" , "glossary" , "Lexicon" , "Brewer's creation, say" .)

I've seen this clue in The Times.

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