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®

forewarning
     n : an early warning about a future event [syn: {premonition}]