Etymology of Abacus
The Cambridge History of the English Language and Linguists Across Historical and Geographical Boundaries both claim that the word Abacus dates before 1387. Middle English writers of that time started calling the sand-board calculators used by Arabs by its Latin name, Abacus.
It has Semitic, Greek and Latin origins, where it was known as abax (in Latin); ἄβαξ in Ancient Greek; Hebrew āvāq (אבק).
Hogg, Richard M. The Cambridge History of the English Language. Cambridge: Cambridge University Press, 1992.
Jackson, Howard. Lexicography an Introduction. London: Routledge, 2002.
Kastovsky, Dieter. Linguistic Theory and Historical Linguistics. Berlin: Mouton De Gruyter, 1986.