Source : Webster's Revised Unabridged Dictionary (1913)

Necessary \Nec"es*sa*ry\, n.; pl. {Necessaries}.
   1. A thing that is necessary or indispensable to some
      purpose; something that one can not do without; a
      requisite; an essential; -- used chiefly in the plural;
      as, the necessaries of life.

   2. A privy; a water-closet.

   3. pl. (Law) Such things, in respect to infants, lunatics,
      and married women, as are requisite for support suitable
      to station.

Necessary \Nec"es*sa*ry\, a. [L. necessarius, from necesse
   unavoidable, necessary; of uncertain origin: cf. F.
   n['e]cessaire.]
   1. Such as must be; impossible to be otherwise; not to be
      avoided; inevitable.

            Death, a necessary end, Will come when it will come.
                                                  --Shak.

   2. Impossible to be otherwise, or to be dispensed with,
      without preventing the attainment of a desired result;
      indispensable; requiste; essential. ``'T is necessary he
      should die.'' --Shak.

            A certain kind of temper is necessary to the
            pleasure and quiet of our minds.      --Tillotson.

   3. Acting from necessity or compulsion; involuntary; --
      opposed to {free}; as, whether man is a necessary or a
      free agent is a question much discussed.

Source : WordNet®

necessary
     adj 1: absolutely essential [ant: {unnecessary}]
     2: unavoidably determined by prior circumstances; "the
        necessary consequences of one's actions"
     n : anything indispensable; "food and shelter are necessities of
         life"; "the essentials of the good life"; "allow farmers
         to buy their requirements under favorable conditions"; "a
         place where the requisites of water fuel and fodder can
         be obtained" [syn: {necessity}, {essential}, {requirement},
          {requisite}] [ant: {inessential}]