Belief in cold grass (5)
I believe the answer is:
creed
'belief' is the definition.
(creed is a kind of belief)
'cold grass' is the wordplay.
'cold' becomes 'c' (eg on taps).
'grass' becomes 'reed' (I've seen this before).
'c'+'reed'='CREED'
'in' acts as a link.
(Other definitions for creed that I've seen before include "restricted set of principles" , "System of belief, faith" , "Religious doctrine" , "Articles of faith" , "Church doctrine" .)