Source : Webster's Revised Unabridged Dictionary (1913)

Weathercock \Weath"er*cock`\, n.
   1. A vane, or weather vane; -- so called because originally
      often in the figure of a cock, turning on the top of a
      spire with the wind, and showing its direction. ``As a
      wedercok that turneth his face with every wind.''
      --Chaucer.

            Noisy weathercocks rattled and sang of mutation.
                                                  --Longfellow.

   2. Hence, any thing or person that turns easily and
      frequently; one who veers with every change of current
      opinion; a fickle, inconstant person.

Weathercock \Weath"er*cock`\, v. t.
   To supply with a weathercock; to serve as a weathercock for.

         Whose blazing wyvern weathercock the spire. --Tennyson.

Source : WordNet®

weathercock
     n : weathervane with a vane in the form of a rooster