Modelling material (4)
(Other definitions for clay that I've seen before include "Soil for moulding" , "Moulding material" , "Brick/pottery substance" , "Earthenware" , "Human body" .)
'modelling material' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for papier mache that I've seen before include "material for craftwork" , "material for moulds" , "Material moulded when wet" , "Pulp which can be painted when dry" .)