A colleague and I were having a discussion as to the proper plural form of abacus. I believe the plural would be abacuses and he feels that the proper form would be abaci. I believe that abacuses is more appropriate as it derives from the root word and abaci is a forked word that is part of the Arabic language.

Any opinions or history to this matter would be appreciated.

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    While the word abacus does indeed originate in the Semitic languages (which include Arabic), it comes to us through Latin. From the Oxford dictionaries on-line: Origin: late Middle English (denoting a board strewn with sand on which to draw figures): from Latin, from Greek abax, abak- 'slab, drawing board', of Semitic origin; probably related to Hebrew 'āḇāq 'dust' Commented Aug 17, 2011 at 22:17

2 Answers 2


As RGW1976 said, both abacuses and abaci are correct. Arabic has nothing to do with the matter: the English word abacus is a direct borrowing of Latin abacus, so it comes with the Latin plural abaci. It also forms the native English plural abacuses. Other examples of this two-plurals phenomenon are the plurals appendixes and appendices, formulas and formulae, and indexes and indices.

In case you’re curious, the Latin word is itself a borrowing of abakos, the genitive of Greek abax 'counting board'. This in turn is probably a borrowing of Hebrew ’ābāq 'dust', so the word may in fact have Arabic relatives, but they have absolutely no bearing on how it forms its plural in English.

  • Excellent, I didn't know it was based on the Greek genitive. Ernout compares it to delphinus, elephantus, and trigonus. Commented Aug 23, 2011 at 3:18
  • I'd guess it's more likely a borrowing from Phoenician than Hebrew, since the Phoenicians were the traders. Commented Sep 30, 2012 at 23:54

According to Merriam-Webster, "abacus" has two proper plural forms: abaci and abacuses.

Looks like you were both correct!

Personally, I would tend to use your choice of "abacuses" over "abaci" as I think the latter could be confusing to some.

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