Put under cold earth (4)
I believe the answer is:
clay
'earth' is the definition.
(clay is a kind of earth)
'put under cold' is the wordplay.
'put' becomes 'lay' ('lay' can be a synonym of 'put').
'under' is a charade indicator (letters next to each other).
'cold' becomes 'c' (eg on taps).
'lay' put after 'c' is 'CLAY'.
(Other definitions for clay that I've seen before include "Material used by potter" , "Soil for moulding" , "Sticky earth; human substance (poet.)" , "Type of soil used in ceramics" , "Heavy soil" .)