From Longman Dictionary of Contemporary Englishabacusab‧a‧cus /ˈæbəkəs/ noun [countable] HMa frame with small balls that can be slid along on thick wires, used for counting and calculatingExamples from the Corpus

abacus• She gave him an abacus, explained the basic principles, and showed him how to make his trick work even better.• Make an abacus and write a report about its usefulness in terms of place value and computation.• Sometimes he calculates the price on an abacus and then indicates the total.• All of them will make either a slide rule or an abacus as a way of presenting how number sets work.• Vassily Prokofyevich, the manager, was doing his accounts, snapping his abacus.• Vocabulary is words, lists of, abacus beads, each encapsulating a precise idea.• Once in a while, the numbers fall, the abacus clicks into a pattern.• The central volutes intertwine and a tendril and foliage breaks the line of the abacus between these and the angle volutes.