The Collaborative International Dictionary of English v.0.48:

Shade \Shade\, v. t. [imp. & p. p. Shaded; p. pr. & vb. n.
   Shading.]
   1. To shelter or screen by intercepting the rays of light; to
      keep off illumination from. --Milton.
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            I went to crop the sylvan scenes,
            And shade our altars with their leafy greens.
                                                  --Dryden.
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   2. To shelter; to cover from injury; to protect; to screen;
      to hide; as, to shade one's eyes.
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            Ere in our own house I do shade my head. --Shak.
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   3. To obscure; to dim the brightness of.
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            Thou shad'st
            The full blaze of thy beams.          --Milton.
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   4. To pain in obscure colors; to darken.
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   5. To mark with gradations of light or color.
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   6. To present a shadow or image of; to shadow forth; to
      represent. [Obs.]
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            [The goddess] in her person cunningly did shade
            That part of Justice which is Equity. --Spenser.
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The Collaborative International Dictionary of English v.0.48:

Shading \Shad"ing\, n.
   1. Act or process of making a shade.
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   2. That filling up which represents the effect of more or
      less darkness, expressing rotundity, projection, etc., in
      a picture or a drawing.
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WordNet (r) 3.0 (2006):

shading
    n 1: graded markings that indicate light or shaded areas in a
         drawing or painting
    2: a gradation involving small or imperceptible differences
       between grades [syn: shading, blending]