In etymology, a primitive word from which spring other words.

In logarithms, the base of any system of logarithms, or that number whose logarithm is unity. Thus in Briggs’, or the common system of logarithms, the radix is 10; in Napier’s, it is 2.7182818284. All other numbers are considered as some powers or roots of the radix, the exponents of which powers or roots, constitute the logarithms of those numbers respectively.

In algebra, radix sometimes denotes the root of a finite expression, from which a series is derived.