1200-50; < Latinarithmētica, feminine singular of arithmēticus < Greekarithmētikḗ (téchnē) (art, skill) of numbers, equivalent to arithmé(ein) to reckon + -t(o)- verbal adjective + -ikḗ-ic; replacing Middle Englisharsmet(r)ike < Old Frencharismetique < Medieval Latinarismētica, with s for Late Greekth
mid-13c., from O.Fr. arsmetique (12c.), from L. arithmetica, from Gk. arithmetike (tekhne) "(the) counting (art)," from arithmos "number," from PIE base *ri- "number" (cf. O.E., O.H.G. rim "number;" O.Ir. rim "number," dorimu "I count;" L. ritus "religious custom"). Originally in English arsmetrik, on folk etymology from L. ars metrica; spelling corrected early 16c. Replaced native tælcræft "tell-craft."