Source : Webster's Revised Unabridged Dictionary (1913)

Twelve \Twelve\, n.
   1. The number next following eleven; the sum of ten and two,
      or of twice six; twelve units or objects; a dozen.

   2. A symbol representing twelve units, as 12, or xii.

   {The Twelve} (Script.), the twelve apostles. --Matt. xxvi.
      20.

Twelve \Twelve\, a. [OE. twelve, twelf, AS. twelf; akin to
   OFries. twelf, twelef, twilif, OS. twelif, D. twaalf, G.
   zw["o]lf, OHG. zwelif, Icel. t?lf, Sw. tolf, Dan. tolv, Goth.
   twalif, from the root of E. two + the same element as in the
   second part of E. eleven. See {Two}, and {Eleven}.]
   One more that eleven; two and ten; twice six; a dozen.

   {Twelve-men's morris}. See the Note under {Morris}.

   {Twelve Tables}. (Rom. Antiq.) See under {Table}.

Source : WordNet®

twelve
     adj : denoting a quantity consisting of 12 items or units [syn: {12},
            {xii}, {dozen}]

twelve
     n : the cardinal number that is the sum of eleven and one [syn:
         {12}, {XII}, {dozen}]