Source : Webster's Revised Unabridged Dictionary (1913)

Beware \Be*ware"\, v. i. [Be, imperative of verb to be + ware.
   See {Ware}, {Wary}.]
   1. To be on one's guard; to be cautious; to take care; --
      commonly followed by of or lest before the thing that is
      to be avoided.

            Beware of all, but most beware of man ! --Pope.

            Beware the awful avalanche.           --Longfellow.

   2. To have a special regard; to heed. [Obs.]

            Behold, I send an Angel before thee. . . . Beware of
            him, and obey his voice.              --Ex. xxiii.
                                                  20, 21.

   Note: This word is a compound from be and the Old English
         ware, now wary, which is an adjective. ``Be ye war of
         false prophetis.'' --Wyclif, Matt. vii. 15. It is used
         commonly in the imperative and infinitive modes, and
         with such auxiliaries (shall, should, must, etc.) as go
         with the infinitive.

Beware \Be*ware"\ (b[-e]*w[^a]r"), v. t.
   To avoid; to take care of; to have a care for. [Obs.]
   ``Priest, beware your beard.'' --Shak.

         To wish them beware the son.             --Milton.

Source : WordNet®

beware
     v : be on one's guard; be cautious or wary about; be alert to;
         "Beware of telephone salesmen" [syn: {mind}]