Source : Webster's Revised Unabridged Dictionary (1913)

Flightiness \Flight"i*ness\, n.
   The state or quality of being flighty.

         The flightness of her temper.            --Hawthorne.

   Syn: Levity; giddiness; volatility; lightness; wildness;
        eccentricity. See {Levity}.

Source : WordNet®

flightiness
     n : the trait of acting unpredictably and more from whim or
         caprice than from reason or judgment; "I despair at the
         flightiness and whimsicality of my memory" [syn: {arbitrariness},
          {whimsicality}, {whimsy}, {whimsey}, {capriciousness}]