AB'ACUS, n. [L. anything flat, as a cupboard, a bench, a slate, a table or board for games; Gr. Usually deduced from the Oriental, abak, dust, because the ancients used tables covered with dust for making figures and diagrams.] 1. Among the Romans, a cupboard or buffet.2. An instrument to facilitate operations in arithmetic; on this are drawn lines; a counter on the lowest line, is one; on the next, ten; on the third, a hundred, &e. On the spaces, counters denote half the number of the line above. Other schemes are called by the same name. The name is also given to a table of numbers, cast up as an abacus of addition; and by analogy, to the art of numbering, as in Knighton's Chronicon.3. In architecture, a table constituting the upper member or crowning of a column and its capital. It is usually square, but sometimes its sides are arched inwards. The name is also given to a concave molding on the capital of the Tuscan pedestal; and to the plinth above the boultin in the Tuscan and Doric orders.
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