Source : Webster's Revised Unabridged Dictionary (1913)

Shady \Shad"y\, a. [Compar. {Shadier}; superl. {Shadiest}.]
   1. Abounding in shade or shades; overspread with shade;
      causing shade.

            The shady trees cover him with their shadow. --Job.
                                                  xl. 22.

            And Amaryllis fills the shady groves. --Dryden.

   2. Sheltered from the glare of light or sultry heat.

            Cast it also that you may have rooms shady for
            summer and warm for winter.           --Bacon.

   3. Of or pertaining to shade or darkness; hence, unfit to be
      seen or known; equivocal; dubious or corrupt. [Colloq.]
      ``A shady business.'' --London Sat. Rev.

            Shady characters, disreputable, criminal. --London
                                                  Spectator.

   {On the shady side of}, on the thither side of; as, on the
      shady side of fifty; that is, more than fifty. [Colloq.]
      

   {To keep shady}, to stay in concealment; also, to be
      reticent. [Slang]

Source : WordNet®

shady
     adj 1: of businesses and businessmen; "a fly-by-night operation"
            [syn: {fly-by-night}]
     2: of questionable taste or morality; "a louche nightclub"; "a
        louche painting" [syn: {louche}]
     3: not as expected; "there was something fishy about the
        accident"; "up to some funny business"; "some definitely
        queer goings-on"; "a shady deal"; "her motives were
        suspect"; "suspicious behavior" [syn: {fishy}, {funny}, {queer},
         {suspect}, {suspicious}]
     4: filled with shade; "the shady side of the street"; "the
        surface of the pond is dark and shadowed"; "we sat on
        rocks in a shadowy cove"; "cool umbrageous woodlands"
        [syn: {shadowed}, {shadowy}, {umbrageous}]
     [also: {shadiest}, {shadier}]