Meaning

noun a tablet placed horizontally on top of the capital of a column as an aid in supporting the architrave

noun a calculator that performs arithmetic functions by manually sliding counters on rods or in grooves

originFrom Late Middle English abacus, abagus, agabus (“abacus; art of counting with an abacus”), from Latin abacus, abax (“sideboard or table with a slab at the top; slab at the top of a column; counting board, sand table; board for playing games”) (compare Late Latin abacus (“art of arithmetic”)), from Ancient Greek ἄβαξ (ábax, “slab, counting board; board covered with sand for drawing; plate;…

Etymology from Wiktionary, CC BY-SA 3.0