abacus

Origin

From 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; dice-board”). Doublet of abaque and abac. The plural form abaci is reinforced from Latin abacī.