American Heritage Dictionary
(3)
Century Dictionary
(10)
GNU Webster's 1913
(1)
WordNet
(2)
Elsewhere on the web
Or are the US album charts counted by hand, using huge ledgers and abacuses?— No Rock And Roll Fun
Nerdly joy in the knowledge that the plural of "abacus" is "abacuses"— Schmutzie.com
Listen to me, Sara Face Alternative, I would need a varsity team of 102 math-club geeks plucking away at their abacuses for 84 weeks to calculate that number.— Boston Phoenix - thePhoenix.com
The abacuses used by the district have 10 rows, each with 10 beads, which help children understand place value in the base-10 numbering system.
She passed out small abacuses to each student and worked with them as she demonstrated double-digit numbers and simple addition.

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