Prevent Bill's daughter leaving (5)

I believe the answer is:

avert

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'prevent' is the definition.
(I know that avert is a more specific form of prevent)

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for avert that I've seen before include "Turn away or aside" , "Parry" , "Deflect away" , "Turn aside, prevent" , "Ward off, deflect" .)

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