Thin slab of ceramic or slate (4)
I believe the answer is:
tile
'thin slab of ceramic or slate' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for tile that I've seen before include "Roofing slab" , "Thin slab used to cover roof, wall, floor etc" , "Flat piece of ceramic" , "9 for the roof?" , "Mah-jong piece" .)