Source : Webster's Revised Unabridged Dictionary (1913)

Warning \Warn"ing\, a.
   Giving previous notice; cautioning; admonishing; as, a
   warning voice.

         That warning timepiece never ceased.     --Longfellow.

   {Warning piece}, {Warning wheel} (Horol.), a piece or wheel
      which produces a sound shortly before the clock strikes.

Warning \Warn"ing\, n.
   1. Previous notice. ``At a month's warning.'' --Dryden.

            A great journey to take upon so short a warning.
                                                  --L'Estrange.

   2. Caution against danger, or against faults or evil
      practices which incur danger; admonition; monition.

            Could warning make the world more just or wise.
                                                  --Dryden.

Warn \Warn\, v. t. [imp. & p. p. {Warned}; p. pr. & vb. n.
   {Warning}.] [OE. warnen, warnien, AS. warnian, wearnian, to
   take heed, to warn; akin to AS. wearn denial, refusal, OS.
   warning, wernian, to refuse, OHG. warnen, G. warnen to warn,
   OFries. warna, werna, Icel. varna to refuse; and probably to
   E. wary. ????.]
   1. To make ware or aware; to give previous information to; to
      give notice to; to notify; to admonish; hence, to notify
      or summon by authority; as, to warn a town meeting; to
      warn a tenant to quit a house. ``Warned of the ensuing
      fight.'' --Dryden.

            Cornelius the centurion . . . was warned from God by
            an holy angel to send for thee.       --Acts x. 22.

            Who is it that hath warned us to the walls? --Shak.

   2. To give notice to, of approaching or probable danger or
      evil; to caution against anything that may prove
      injurious. ``Juturna warns the Daunian chief of Lausus'
      danger, urging swift relief.'' --Dryden.

   3. To ward off. [Obs.] --Spenser.

Source : WordNet®

warning
     n 1: a message informing of danger
     2: cautionary advice about something imminent (especially
        imminent danger) [syn: {admonition}, {monition}, {word of
        advice}]

warning
     adj : serving to warn; "shook a monitory finger at him"; "an
           exemplary jail sentence" [syn: {admonitory}, {cautionary},
            {exemplary}, {monitory}, {warning(a)}]