Flat piece of ceramic (4)
I believe the answer is:
tile
'flat piece of ceramic' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for tile that I've seen before include "Flat thin slab of clay, for example" , "Thin slab used to cover roof, wall, floor etc" , "Small slab of baked clay for covering walls, roofs etc" , "Ceramic rectangle" , "Thin slab of ceramic or slate" .)