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.

Source : WordNet®

zero
     v 1: adjust (an instrument or device) to zero value
     2: adjust (as by firing under test conditions) the zero of (a
        gun); "He zeroed in his rifle at 200 yards" [syn: {zero in}]
     [also: {zeroes} (pl)]

zero
     n 1: a quantity of no importance; "it looked like nothing I had
          ever seen before"; "reduced to nil all the work we had
          done"; "we racked up a pathetic goose egg"; "it was all
          for naught"; "I didn't hear zilch about it" [syn: {nothing},
           {nil}, {nix}, {nada}, {null}, {aught}, {cipher}, {cypher},
           {goose egg}, {naught}, {zilch}, {zip}]
     2: a mathematical element that when added to another number
        yields the same number [syn: {0}, {nought}, {cipher}, {cypher}]
     3: the quantity that registers a reading of zero on a scale
        [syn: {zero point}]
     [also: {zeroes} (pl)]

zero
     adj 1: indicating the absence of any or all units under
            consideration; "a zero score" [syn: {0}]
     2: indicating an initial point or origin
     3: of or relating to the null set (a set with no members)
     4: having no measurable or otherwise determinable value; "the
        goal is zero population growth" [syn: {zero(a)}]
     [also: {zeroes} (pl)]

zeroes
     See {zero}