Flat piece of ceramic (4)
I believe the answer is:
tile
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">flat piece of ceramic</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(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" .)