a tablet placed horizontally on top of the capital of a column as an aid in supporting the architrave
"The ancient architect carefully positioned the marble abacus atop the towering column to ensure it would properly support the heavy stone architrave above."
a calculator that performs arithmetic functions by manually sliding counters on rods or in grooves
"The accountant relied on an old-fashioned abacus to calculate the day's sales before the power grid failed."
A table or tray scattered with sand which was used for calculating or drawing.
"The ancient scribe wiped away his calculations from the abacus, a shallow wooden tray filled with fine river sand where he had been dividing rations by tracing lines in the dust."
The word "abacus" comes from the Latin abacus, which originally meant a sideboard or a counting board. This term was borrowed from Ancient Greek, where it referred to a slab or a board covered with sand used for drawing and games.