Cash book's limitless margin (4)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
edge
'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" .)