1.AdverbIn a way characterized by addition (of increments) rather than multiplication (by factors) or exponentiation (by exponents): by an arithmetic progression.
"Over the past decade the business has grown arithmetically, which shows that it is serving a demand successfully; but because it has not grown exponentially, its growth is viewed by some investors as "not good enough.""
2.AdverbIn terms of arithmetic.
"The two terms are arithmetically equivalent, but they are not equally intuitive regarding what phenomenon they represent in the real world."