Source : Webster's Revised Unabridged Dictionary (1913)

Sudden \Sud"den\, n.
   An unexpected occurrence; a surprise.

   {All of a sudden}, {On a sudden}, {Of a sudden}, sooner than
      was expected; without the usual preparation; suddenly.

            How art thou lost! how on a sudden lost! --Milton.

            He withdrew his opposition all of a sudden.
                                                  --Thackeray.

Sudden \Sud"den\, a. [OE. sodian, sodein, OF. sodain, sudain, F.
   soudain, L. subitaneus, fr. subitus sudden, that has come
   unexpectedly, p. p. of subire to come on, to steal upon; sub
   under, secretly + ire to go. See {Issue}, and cf.
   {Subitaneous}.]
   1. Happening without previous notice or with very brief
      notice; coming unexpectedly, or without the common
      preparation; immediate; instant; speedy. ``O sudden wo!''
      --Chaucer. ``For fear of sudden death.'' --Shak.

            Sudden fear troubleth thee.           --Job xxii.
                                                  10.

   2. Hastly prepared or employed; quick; rapid.

            Never was such a sudden scholar made. --Shak.

            The apples of Asphaltis, appearing goodly to the
            sudden eye.                           --Milton.

   3. Hasty; violent; rash; precipitate. [Obs.] --Shak.

   Syn: Unexpected; unusual; abrupt; unlooked-for. --
        {Sud"den*ly}, adv. -- {Sud"den*ness}, n.

Sudden \Sud"den\, adv.
   Suddenly; unexpectedly. [R.]

         Herbs of every leaf that sudden flowered. --Milton.

Source : WordNet®

sudden
     adj : happening without warning or in a short space of time; "a
           sudden storm"; "a sudden decision"; "a sudden cure"
           [ant: {gradual}]