adjective

1. made up of two parts or things; twofold; double
2. designating or of a number system in which the base used is two, each number being expressed in powers of two by using only two digits, specif. 0 and 1
3. designating or of a musical form consisting of two closely related sections
4. Chem. composed of two elements or radicals, or of one element and one radical binary compounds

Etymology: ME binarie < L binarius < bini, two by two < bis, double < IE *duis < base *dwōu-, two

noun pl. binaries -·ries

1. something made up of two parts or things
2. binary star