The Collaborative International Dictionary of English v.0.48:
Shady \Shad"y\, a. [Compar. Shadier; superl. Shadiest.]
1. Abounding in shade or shades; overspread with shade;
The shady trees cover him with their shadow. --Job.
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; of questionable character; unsavory;
equivocal; dubious, corrupt, or criminal; as, a shady
character; -- of people or activities. [Colloq.] "A shady
business." --London Sat. Rev.
Shady characters, disreputable, criminal. --London
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