In
architecture, an
abacus (from the
Greek abax, slab; or French
abaque,
tailloir; plural
abacuses or
abaci) is a flat slab forming the uppermost member or division of the
capital of a
column, above the
bell. Its chief function is to provide a large supporting surface, tending to be wider than the capital, to receive the weight of the
arch or the
architrave above. The diminutive of abacus,
abaculus, is used to describe small
mosaic tiles, also called
abaciscus or
tessera, used to create ornamental floors with detailed patterns of chequers or squares in a
tessellated pavement.