The Collaborative International Dictionary of English v.0.48:

Flightiness \Flight"i*ness\, n.
   The state or quality of being flighty.
   [1913 Webster]

         The flightness of her temper.            --Hawthorne.

   Syn: Levity; giddiness; volatility; lightness; wildness;
        eccentricity. See Levity.
        [1913 Webster]

WordNet (r) 3.0 (2006):

flightiness
    n 1: 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:
         flightiness, arbitrariness, whimsicality, whimsy,
         whimsey, capriciousness]