Abacus, (ab'a-kus). [L. abacus, table.] 1. The upper plata of a column, beneath the architrave. 2. A calculating apparatus. Abacus.
A'BACUS (a counter, a chessboard). An ancient instrument for aiding numerical calculations. The Greek abacus consisted of an oblong frame, having wires stretched across it, carrying perforated ivory balls. In the Roman abacus, the counters were slid along grooves.