Abacus. (1) An instrument sometimes used to facilitate arithmetical calculations in infant schools; it is made of parallel wires, on which are strung beads of various colours. It was used in Greece and in Rome, and is still employed in China, where it is known as Shwanpan.
(2) In architecture, an abacus is a flat stone (Lat. abacus, a cushion) crowning the capital of a column. In the Tuscan, Doric, and ancient Ionic styles, it was square or flat; in the Corinthian and Composite orders, as well as in some of the later Ionic, the sides were hollowed and the angles truncated.