Source : Webster's Revised Unabridged Dictionary (1913)

Vision \Vi"sion\, n. [OE. visioun, F. vision, fr. L. visio, from
   videre, visum, to see: akin to Gr. ? to see, ? I know, and E.
   wit. See {Wit}, v., and cf. {Advice}, {Clairvoyant}, {Envy},
   {Evident}, {Provide}, {Revise}, {Survey}, {View}, {Visage},
   {Visit}.]
   1. The act of seeing external objects; actual sight.

            Faith here is turned into vision there. --Hammond.

   2. (Physiol.) The faculty of seeing; sight; one of the five
      senses, by which colors and the physical qualities of
      external objects are appreciated as a result of the
      stimulating action of light on the sensitive retina, an
      expansion of the optic nerve.

   3. That which is seen; an object of sight. --Shak.

   4. Especially, that which is seen otherwise than by the
      ordinary sight, or the rational eye; a supernatural,
      prophetic, or imaginary sight; an apparition; a phantom; a
      specter; as, the visions of Isaiah.

            The baseless fabric of this vision.   --Shak.

            No dreams, but visions strange.       --Sir P.
                                                  Sidney.

   5. Hence, something unreal or imaginary; a creation of fancy.
      --Locke.

   {Arc of vision} (Astron.), the arc which measures the least
      distance from the sun at which, when the sun is below the
      horizon, a star or planet emerging from his rays becomes
      visible.

   {Beatific vision} (Theol.), the immediate sight of God in
      heaven.

   {Direct vision} (Opt.), vision when the image of the object
      falls directly on the yellow spot (see under {Yellow});
      also, vision by means of rays which are not deviated from
      their original direction.

   {Field of vision}, field of view. See under {Field}.

   {Indirect vision} (Opt.), vision when the rays of light from
      an object fall upon the peripheral parts of the retina.

   {Reflected vision}, or {Refracted vision}, vision by rays
      reflected from mirrors, or refracted by lenses or prisms,
      respectively.

   {Vision purple}. (Physiol.) See {Visual purple}, under
      {Visual}.

Source : WordNet®

field of vision
     n : all of the points of the physical environment that can be
         perceived by a stable eye at a given moment [syn: {visual
         field}, {field of regard}]