Right of the keeper (4)

I believe the answer is:

lien

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'right' is the definition.
(legal right)

I don't understand the remainder of the clue.

(Other definitions for lien that I've seen before include "Security for a debt" , "Right to a lawyer" , "The right to take property if an obligation is not met" , "Legal right to detain property" , "Legal claim on the property of another" .)

I've seen this clue in the Evening Standard.

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