Butler who wrote a book (6)

I believe the answer is:

samuel

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'butler' is the definition.
(I know that butler given name Samuel)

I cannot understand how the rest of the clue works.

(Other definitions for samuel that I've seen before include "XWD SETTER" , "Two books of the Bible bear this name" , "Hebrew prophet" , "First name of Beckett, Irish writer" , "-- Beckett, Irish dramatist" .)

I've seen this clue in The Independent.

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