Intro missing from fact book (4)

I believe the answer is:

ruth

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'book' is the definition.
(book of the Bible)

I don't understand the rest of the clue.

(Other definitions for ruth that I've seen before include "Damsel" , "Old word for pity, or Bible book" , "Girl" , "Girl's name; pity (archaic)" , "Babe -, US baseball star" .)

I've seen this clue in The Times.

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