[1] : The Collaborative International Dictionary of English v.0.48

beware \beware"\, 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.
      1913 webster

            beware of all, but most beware of man  --pope.
      1913 webster

            beware the awful avalanche.           --longfellow.
      1913 webster

   2. to have a special regard; to heed. obs.
      1913 webster

            behold, i send an angel before thee. . . . beware of
            him, and obey his voice.              --ex. xxiii.
                                                  20, 21.
      1913 webster

   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.
         1913 webster
see also:
ware wary 

[2] : The Collaborative International Dictionary of English v.0.48

beware \beware"\ b-ew^ar", v. t.
   to avoid; to take care of; to have a care for. obs.
   "priest, beware your beard." --shak.
   1913 webster

         to wish them beware the son.             --milton.
   1913 webster

[3] : WordNet (r) 2.0

beware
     v : be on one's guard; be cautious or wary about; be alert to;
         "beware of telephone salesmen" syn: mind
see also:
mind 

Beware >> B Words
Beware, definition of term: Beware
beware_pag1.html

Beware Of >> B Words
Beware Of, definition of term: Beware Of
beware+of_pag1.html