Arithmetical is one of the adjectival forms of arithmetic.
Also known as
The other adjectival forms of arithmetical is arithmetic, with the stress on the first and third syllables.
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.