Pl. abaci. [a. L. abacus, f. Gr. ἄβαξ a board or slab, a draughtboard, a calculating, table, a sideboard, a plate, &c. Used in Eng. in several of the Gr. and L. meanings.]
† 1. A board or tray strewn with sand, for the delineation of figures, geometrical diagrams, etc. Obs.
1387. Trevisa, Higden’s Polychr. (Rolls Ser.), VII. 69. Abacus is a table wiþ þe whiche schappes beþ portrayed and ipeynt in powdre, and abacus is a craft of geometrie. [Not in the original Higden.]
2. A calculating table, or frame; spec. one in which balls slide upon wires, and gen. any arrangement for the mechanical solution of arithmetical problems.
1686. Obs. conc. Chinese Char., in Misc. Cur., III. 216. Their Abacus or counting Board, for performing the Operations of Arithmetick, which I find pretty near to agree with that of the antient Romans.
1861. T. Wright, Ess. on Archæol., II. xv. 67. The system of the abacus appears to have continued in use … till late in the twelfth century.
1871. Earle, Philol. Eng. Tongue, 353. The science of calculation by nine figures and zero, which was gradually superseding the abacus or ball-frame, with its counters.
1881. Nature, No. 625, 593. M. Gariel has thus arrived at a kind of abacus by which the various problems that arise may be geometrically solved by simple inspection.
3. Arch. The upper member of the capital of a column, supporting the architrave; in the Tuscan, Doric, and ancient Ionic orders, a square flat plate, but in the Corinthian and Composite, variously cut and ornamented.
1563. Shute, Architecture, iv. 2a. The Abacus, that lieth upon Voluta, is iust .4. square flat like to a trencher.
1664. Evelyn, trans. Freart, Parallel of Arch., 129. The Abacus … is that quadrangular piece … serving instead of a Corona or drip to the Capitel.
1760. Raper, in Phil. Trans., LI. 797. The pointed abacus shews the architecture to be Greek.
1879. Scott, Lect. on Archit., I. 127. The crochet capital, which is magnificently developed beneath round abaci.
† 4. = ABACK, sb. Obs. (perh. never used in Eng.)
5. Gr. & Rom. Antiq. A side-board.
1853. Soyer, Pantroph., 264. The most precious plate is arranged before the arrival of the guests, on the abacus, or sideboard.
