We don't have synonyms for arith yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are frith, brith and grith.
(n) :
Abbreviation of arithmetic. [The mathematics of numbers (integers, rational numbers, real numbers, or complex numbers) under the operations of addition, subtraction, multiplication, and division.]
(n) :
Abbreviation of arithmetic. [The mathematics of numbers (integers, rational numbers, real numbers, or complex numbers) under the operations of addition, subtraction, multiplication, and division.]