Slate (4)
I believe the answer is:
tile
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">slate</span>' is the definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for tile that I've seen before include "Roofing slab" , "Roofing material" , "Ceramic rectangle" , "Flat thin slab of clay, for example" , "Roof slabs" .)