Cash book's limitless margin (4)

I believe the answer is:

edge

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'margin' is the definition.
(synonyms)

'cash book's limitless' is the wordplay.
'cash' becomes 'e' (I can't justify this - if you can you should believe this answer much more).
'book's' becomes 'Judges's' (book of the Old Testament).
'limitless' says to take the centre.
The centre of 'judgess' is 'dge'.
'e'+'dge'='EDGE'

Can you help me to learn more?

(Other definitions for edge that I've seen before include "Rim,border" , "Golden ingot" , "Intense quality; limit" , "Rim or sharp side of knife" , "Lip; advantage" .)

I've seen this clue in The Independent.

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