The Collaborative International Dictionary of English v.0.48:

Sky \Sky\ (sk[imac]), n.; pl. Skies (sk[imac]z). [OE. skie a
   cloud, Icel. sk[=y]; akin to Sw. & Dan. sky; cf. AS. sc[=u]a,
   sc[=u]wa, shadow, Icel. skuggi; probably from the same root
   as E. scum. [root]158. See Scum, and cf. Hide skin,
   Obscure.]
   1. A cloud. [Obs.]
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            [A wind] that blew so hideously and high,
            That it ne lefte not a sky
            In all the welkin long and broad.     --Chaucer.
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   2. Hence, a shadow. [Obs.]
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            She passeth as it were a sky.         --Gower.
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   3. The apparent arch, or vault, of heaven, which in a clear
      day is of a blue color; the heavens; the firmament; --
      sometimes in the plural.
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            The Norweyan banners flout the sky.   --Shak.
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   4. The wheather; the climate.
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            Thou wert better in thy grave than to answer with
            thy uncovered body this extremity of the skies.
                                                  --Shak.
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   Note: Sky is often used adjectively or in the formation of
         self-explaining compounds; as, sky color, skylight,
         sky-aspiring, sky-born, sky-pointing, sky-roofed, etc.
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   Sky blue, an azure color.

   Sky scraper (Naut.), a skysail of a triangular form.
      --Totten.

   Under open sky, out of doors. "Under open sky adored."
      --Milton.
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Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "sky blue":
   azure, azure-blue, azure-colored, azurean, azured, azureous,
   beryl-blue, berylline, blue, bluish, cerulean, ceruleous,
   cerulescent, cyanean, dark-blue, deep-blue, light-blue,
   lightish-blue, livid, pavonian, pavonine, peacock-blue, sapphire,
   sapphirine, sky-colored, sky-dyed, turquoise