1. consisting of, indicating, or involving two.
  2. Mathematics.
    1. of or relating 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.
    2. of or relating to the digits or numbers used in binary notation.
    3. of or relating to a binary system.
    4. (of an operation) assigning a third quantity to two given quantities, as in the addition of two numbers.
  3. Computers. of, relating to, or written in binary code; programmed or encoded using only the digits 0 and 1: All executable programs on the computer are stored in binary files.
  4. Chemistry. noting a compound containing only two elements or groups, as sodium chloride, methyl bromide, or methyl hydroxide.
  5. Metallurgy. (of an alloy) having two principal constituents.

noun, plural bi·na·ries.

  1. a whole composed of two.
  2. Mathematics. 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: to convert decimal to binary.
  3. Also called binary number. Mathematics. a number expressed in the binary system of notation.
  4. Computers. binary code.
  5. Computers. an executable file stored in binary format.
  6. Astronomy. binary star.


  1. composed of, relating to, or involving two; dual
  2. maths computing of, relating to, or expressed in binary notation or binary code
  3. (of a compound or molecule) containing atoms of two different elements
  4. metallurgy (of an alloy) consisting of two components or phases
  5. (of an educational system) consisting of two parallel forms of education such as the grammar school and the secondary modern in Britain
  6. maths logic (of a relation, expression, or operation) applying to two elements of its domain; having two argument places; dyadic

noun plural -ries

  1. something composed of two parts or things
  2. astronomy See binary star
  3. short for binary weapon

“dual,” mid-15c., from Late Latin binarius “consisting of two,” from bini “twofold, two apiece, two-by-two” (used especially of matched things), from bis “double” (see bis-). Binary code in computer terminology was in use by 1952, though the idea itself is ancient. Binary star in astronomy is from 1802.


  1. Characterized by or consisting of two parts or components; twofold.
  2. Consisting of or containing only molecules having two kinds of atoms.

  1. Having two parts.
  2. Mathematics Based on the number 2 or the binary number system.

Anything composed of two parts. In modern computers, information is stored in banks of components that act like switches. Since switches can be either on or off, they have a binary character, and we say that the computer uses “binary arithmetic” to do its work.

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