All the ground is deadly! (6)
I believe the answer is:
lethal
'is deadly' is the definition.
('lethal' can be a synonym of 'deadly')
'all the ground' is the wordplay.
'ground' indicates anagramming the letters (grind the letters ).
'all'+'the'='allthe'
'allthe' anagrammed gives 'LETHAL'.
(Other definitions for lethal that I've seen before include "describing a killer?" , "Able to cause death" , "--- Weapon, Mel Gibson film" , "Terminal" , "bringing down the curtain" .)