/ əˈrɪθmətɪk; NAmE / noun [ U ]
1.
the type of mathematics that deals with the adding, multiplying, etc. of numbers :
He's not very good at arithmetic.
2.
sums involving the adding, multiplying, etc. of numbers :
a quick bit of mental arithmetic
I think there's something wrong with your arithmetic.
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WORD ORIGIN
Middle English : from Old French arismetique , based on Latin arithmetica , from Greek arithmētikē (tekhnē) (art) of counting, from arithmos number.