ab·a·cus (ăbə-kəs, ə-băkəs)
n. pl. ab·a·cus·es or ab·a·ci (ăbə-sī′, ə-băkī′)
1. A manual computing device consisting of a frame holding parallel rods strung with movable counters.
2. Architecture A slab on the top of the capital of a column.
[Middle English, from Latin, from Greek abax, abak-, counting board, perhaps from a Semitic source akin to Hebrew 'ābāq, dust; see ʾbq in the Appendix of Semitic roots.]
Word History: The source of our word abacus, the Greek word abax, may have originated in one of the Semitic languages spoken in the ancient Near East. The Semitic word that was the source of Greek abax was probably akin to the Hebrew word 'ābāq, "dust," which in postbiblical usage could also mean "sand used as a writing surface." The Greek word abax has as one of its senses "a board sprinkled with sand or dust for drawing geometric diagrams." Boards like this were also used for performing arithmetic calculations by moving pebbles around the board, and these early abacuses eventually developed into the abacuses with movable counters strung on rods familiar to us today. Greek abax was borrowed into Latin as abacus, and then the Latin word was borrowed into Middle English. The first known use of the word abacus in English, found in a Middle English work written before 1387, refers to a kind of sand-board abacus that was used according to techniques that European mathematicians adopted from the Muslim world.
(click for a larger image)abacus
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.