Edict on new grass (4)
I believe the answer is:
lawn
'grass' is the definition.
(a lawn is an area of grass)
'edict on new' is the wordplay.
'edict' becomes 'law' (I've seen this before).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'law'+'n'='LAWN'
(Other definitions for lawn that I've seen before include "Area of short grass" , "Cultivated and mowed grass" , "Fine fabric" , "Fine cotton or grass garden" , "Area of tended grass" .)