The Collaborative International Dictionary of English v.0.48:

Giddy \Gid"dy\, a. [Compar. Giddier; superl. Giddiest.] [OE.
   gidi mad, silly, AS. gidig, of unknown origin, cf. Norw.
   gidda to shake, tremble.]
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   1. Having in the head a sensation of whirling or reeling
      about; having lost the power of preserving the balance of
      the body, and therefore wavering and inclined to fall;
      lightheaded; dizzy.
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            By giddy head and staggering legs betrayed. --Tate.
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   2. Promoting or inducing giddiness; as, a giddy height; a
      giddy precipice. --Prior.
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            Upon the giddy footing of the hatches. --Shak.
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   3. Bewildering on account of rapid turning; running round
      with celerity; gyratory; whirling.
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            The giddy motion of the whirling mill. --Pope.
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   4. Characterized by inconstancy; unstable; changeable;
      fickle; wild; thoughtless; heedless. "Giddy, foolish
      hours." --Rowe. "Giddy chance." --Dryden.
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            Young heads are giddy and young hearts are warm.
                                                  --Cowper.
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