Abacus (ăb&adot_;kŭs), n.; E. pl. Abacuses ; L. pl. Abaci (-sī). [L. abacus, abax, Gr. 'abax] 1. A table or tray strewn with sand, anciently used for drawing, calculating, etc. [Obs.][1913 Webster]
2. A calculating table or frame; an instrument for performing arithmetical calculations by balls sliding on wires, or counters in grooves, the lowest line representing units, the second line, tens, etc. It is still employed in China.[1913 Webster]
3. (Arch.) (a) The uppermost member or division of the capital of a column, immediately under the architrave. See Column. (b) A tablet, panel, or compartment in ornamented or mosaic work.[1913 Webster]
4. A board, tray, or table, divided into perforated compartments, for holding cups, bottles, or the like; a kind of cupboard, buffet, or sideboard.[1913 Webster]
Abacus harmonicus (Mus.), an ancient diagram showing the structure and disposition of the keys of an instrument. Crabb.[1913 Webster]