Source : Webster's Revised Unabridged Dictionary (1913)

Forewarn \Fore*warn"\, v. t. [imp. & p. p. {Forewarned}; p. pr.
   & vb. n. {Forewarning}.]
   To warn beforehand; to give previous warning, admonition,
   information, or notice to; to caution in advance.

         We were forewarned of your coming.       --Shak.

Source : WordNet®

forewarn
     v : warn in advance or beforehand; give an early warning; "I
         forewarned him of the trouble that would arise if he
         showed up at his ex-wife's house" [syn: {previse}]