Material contained in half a brick (6)
I believe the answer is:
fabric
'material' is the definition.
(I know that material can be written as fabric)
'contained in half a brick' is the wordplay.
'contained in' indicates a hidden word.
'FABRIC' is hidden within 'half a brick'.
(Other definitions for fabric that I've seen before include "Cloth, woven material" , "Building structure; textile" , "Perhaps felt" , "Underlying structure" , "Silk or satin, say" .)