Ruling on new grass (4)

I believe the answer is:

lawn

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'grass' is the definition.
(a lawn is an area of grass)

'ruling on new' is the wordplay.
'ruling on' becomes 'law' (I can't explain this - if you can you should give a lot more credence to this answer).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'law'+'n'='LAWN'

Can you help me to learn more?

(Other definitions for lawn that I've seen before include "Fine fabric" , "material" , "Grass, as for tennis" , "Blades trimmed" , "Type of thin linen or cotton" .)

I've seen this clue in The Daily Express.

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