Turn down book conclusion (4)

I believe the answer is:

bend

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

'turn' is the definition.
(I know that turn can be written as bend)

'down book conclusion' is the wordplay.
'down book' becomes 'b' (abbreviation for book. I am not sure about the 'down' bit.).
'conclusion' becomes 'end' (something's conclusion is its end).
'b'+'end'='BEND'

Can you help me to learn more?

(Other definitions for bend that I've seen before include "Arc" , "elbow" , "Country; bird" , "Form a curve" , "Crouch" .)

I've seen this clue in the Sydney Morning Herald.

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