Son of David Newton soon having day off (6)

I believe the answer is:

nathan

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'son' is the definition.
Both the answer and definition are singular nouns.
Maybe there's a link between them I don't understand?

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for nathan that I've seen before include "Old Testament prophet" , "Boy" , "Wise old merchant" .)

I've seen this clue in The Independent.

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