Floor square (4)
I believe the answer is:
tile
'floor square' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tile that I've seen before include "Flat thin slab of clay, for example" , "Ceramic slab for roofs, walls, floors etc" , "Scrabble piece" , "Ceramic rectangle" , "Thin rectangular slab to cover surfaces" .)