The Collaborative International Dictionary of English v.0.48:

Capricious \Ca*pri"cious\ (k[.a]*pr[i^]sh"[u^]s), a. [Cf. F.
   capricieux, It. capriccioso.]
   Governed or characterized by caprice; apt to change suddenly;
   freakish; whimsical; changeable. "Capricious poet." --Shak.
   "Capricious humor." --Hugh Miller.
   [1913 Webster]

         A capricious partiality to the Romish practices.
                                                  --Hallam.

   Syn: Freakish; whimsical; fanciful; fickle; crotchety;
        fitful; wayward; changeable; unsteady; uncertain;
        inconstant; arbitrary. -- Ca*pri"cious*ly, adv. --
        Ca*pri"cious*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

capriciousness
    n 1: the quality of being guided by sudden unpredictable
         impulses [syn: capriciousness, unpredictability]
    2: 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]