—adj. 1. consisting of, indicating, or involving two.
2. Math. a. of or pertaining to a system of numerical notation to the base 2, in which each place of a number, expressed as 0 or 1, corresponds to a power of 2. The decimal number 58 appears as 111010 in binary notation, since 58 = 1 × 25 + 1 × 24 + 1 × 23 + 0 × 22 + 1 × 21 + 0 × 20.
b. of or pertaining to the digits or numbers used in binary notation.
c. of or pertaining to a binary system.
d. (of an operation) assigning a third quantity to two given quantities, as in the addition of two numbers.
3. Chem.noting a compound containing only two elements or groups, as sodium chloride, methyl bromide, or methyl hydroxide.
4. Metall.(of an alloy) having two principal constituents.
—n. 1. a whole composed of two.
2. Astron.See binary star. 3. Also called bi'nary num'ber.Math.a number expressed in the binary system of notation.