Source : Webster's Revised Unabridged Dictionary (1913)

Zero \Ze"ro\, n.; pl. {Zeros}or {Zeroes}. [F. z['e]ro, from Ar.
   [,c]afrun, [,c]ifrun, empty, a cipher. Cf. {Cipher}.]
   1. (Arith.) A cipher; nothing; naught.

   2. The point from which the graduation of a scale, as of a
      thermometer, commences.

   Note: Zero in the Centigrade, or Celsius thermometer, and in
         the R['e]aumur thermometer, is at the point at which
         water congeals. The zero of the Fahrenheit thermometer
         is fixed at the point at which the mercury stands when
         immersed in a mixture of snow and common salt. In
         Wedgwood's pyrometer, the zero corresponds with
         1077[deg] on the Fahrenheit scale. See Illust. of
         {Thermometer}.

   3. Fig.: The lowest point; the point of exhaustion; as, his
      patience had nearly reached zero.

   {Absolute zero}. See under {Absolute}.

   {Zero method} (Physics), a method of comparing, or measuring,
      forces, electric currents, etc., by so opposing them that
      the pointer of an indicating apparatus, or the needle of a
      galvanometer, remains at, or is brought to, zero, as
      contrasted with methods in which the deflection is
      observed directly; -- called also {null method}.

   {Zero point}, the point indicating zero, or the commencement
      of a scale or reckoning.



   {Absolute zero} (Physics), the be ginning, or zero point, in
      the scale of absolute temperature. It is equivalent to
      -273[deg] centigrade or -459.4[deg] Fahrenheit.

   Syn: Positive; peremptory; certain; unconditional; unlimited;
        unrestricted; unqualified; arbitrary; despotic;
        autocratic.

Source : WordNet®

absolute zero
     n : (cryogenics) the lowest temperature theoretically attainable
         (at which the kinetic energy of atoms and molecules is
         minimal); 0 Kelvin or -273.15 Centigrade or -459.67
         Fahrenheit