The Collaborative International Dictionary of English v.0.48:

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.
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            Faith here is turned into vision there. --Hammond.
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   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.
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   3. That which is seen; an object of sight. --Shak.
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   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.
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            The baseless fabric of this vision.   --Shak.
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            No dreams, but visions strange.       --Sir P.
                                                  Sidney.
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   5. Hence, something unreal or imaginary; a creation of fancy.
      --Locke.
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   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.
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The Collaborative International Dictionary of English v.0.48:

Visual \Vis"u*al\, a. [L. visualis, from visus a seeing, sight:
   cf. F. visuel. See Vision.]
   1. Of or pertaining to sight; used in sight; serving as the
      instrument of seeing; as, the visual nerve.
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            The air,
            Nowhere so clear, sharpened his visual ray.
                                                  --Milton.
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   2. That can be seen; visible. [R.]
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   Visual angle. (Opt.) See under Angle.

   Visual cone (Persp.), a cone whose vertex is at the point
      of sight, or the eye.

   Visual plane, any plane passing through the point of sight.


   Visual point, the point at which the visual rays unite; the
      position of the eye.

   Visual purple (Physiol.), a photochemical substance, of a
      purplish red color, contained in the retina of human eyes
      and in the eyes of most animals. It is quickly bleached by
      light, passing through the colors, red, orange, and
      yellow, and then disappearing. Also called rhodopsin,
      and vision purple. See Optography.

   Visual ray, a line from the eye, or point of sight.

   Visual white (Physiol.), the final product in the action of
      light on visual purple. It is reconverted into visual
      purple by the regenerating action of the choroidal
      epithelium.

   Visual yellow (Physiol.), a product intermediate between
      visual purple and visual white, formed in the
      photochemical action of light on visual purple.
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