Definition:Arithmetic/Linguistic Note

Definition
The word arithmetic, when used as a noun, is pronounced with the stress on the second syllable: a-rith-me-tic.

Its adjectival form, on the other hand, places the stress on the first and third syllables: a-rith-met-ic.

To avoid confusion between the noun and adjective, the adjectival form arithmetical is often used, being pronounced a-rith-met-ic-al.