\Ab"a*cus\ ([a^]b"[.a]*k[u^]s), n.; E. pl. {Abacuses}; L.
pl. {Abaci} (-s[imac]). [L. abacus, abax, Gr. 'a`bax]
1. A table or tray strewn with sand, anciently used for
   drawing, calculating, etc. [Obs.]
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.
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.
4. A board, tray, or table, divided into perforated
   compartments, for holding cups, bottles, or the like; a
   kind of cupboard, buffet, or sideboard.
{Abacus harmonicus} (Mus.), an ancient diagram showing the
   structure and disposition of the keys of an instrument.
   --Crabb.