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):

capricious
    adj 1: changeable; "a capricious summer breeze"; "freakish
           weather" [syn: capricious, freakish]
    2: determined by chance or impulse or whim rather than by
       necessity or reason; "a capricious refusal"; "authoritarian
       rulers are frequently capricious"; "the victim of whimsical
       persecutions" [syn: capricious, impulsive, whimsical]

Moby Thesaurus II by Grady Ward, 1.0:

270 Moby Thesaurus words for "capricious":
   adrift, afloat, agnostic, aimless, alternating, ambiguous,
   ambitendent, ambivalent, amorphous, arbitrary, at loose ends,
   brittle, broken, careening, careless, casual, catchy, chancy,
   changeable, changeful, changing, choppy, corruptible, cranky,
   crotchety, deciduous, desultory, deviable, deviating, deviative,
   deviatory, dicey, different, disarticulated, disconnected,
   discontinuous, disjunct, disordered, disorderly, dispersed,
   disproportionate, divaricate, divergent, diversified, diversiform,
   dizzy, double-minded, doubting, dubious, dying, eccentric,
   effervescent, ephemeral, equivocal, erose, erratic, evanescent,
   fading, fanciful, fantasied, fantastic, fast and loose,
   fence-sitting, fence-straddling, fickle, fitful, flaky, fleeting,
   flickering, flighty, flitting, fluctuant, fluctuating,
   fly-by-night, flying, formless, fragile, frail, freakish,
   frivolous, fugacious, fugitive, giddy, gratuitous, guttering,
   halting, haphazard, harebrained, heedless, herky-jerky, hesitant,
   hesitating, heteroclite, hit-or-miss, humorsome, iffy,
   immethodical, impermanent, impetuous, impulsive, inadvertent,
   incalculable, inchoate, incoherent, inconsiderate, inconsistent,
   inconstant, indecisive, indemonstrable, indiscriminate, infirm,
   infirm of purpose, insubstantial, intermittent, intermitting,
   irregular, irresolute, irresolved, irresponsible, jagged, jerky,
   kinky, lubricious, lurching, maggoty, mazy, meaningless, mercurial,
   misshapen, momentary, moody, mortal, motiveless, motley,
   mugwumpian, mugwumpish, mutable, nonconformist, nondurable,
   nonpermanent, nonstandard, nonsymmetrical, nonsystematic,
   nonuniform, notional, of two minds, orderless, passing, patchy,
   perishable, petulant, planless, pluralistic, polysemous,
   promiscuous, quirky, ragged, rambling, random, reasonless,
   restless, rough, roving, scatterbrained, scrappy, senseless,
   shapeless, shifting, shifty, short-lived, shuffling, skeptical,
   snatchy, spasmatic, spasmic, spasmodic, spastic, spineless,
   sporadic, spotty, staggering, straggling, straggly, systemless,
   temperamental, temporal, temporary, thoughtless, ticklish,
   touch-and-go, transient, transitive, transitory, unaccountable,
   unarranged, uncalculating, uncertain, unclassified, unconfirmable,
   uncontrolled, unconvinced, undecided, undependable, undetermined,
   undirected, undisciplined, undivinable, undurable, unenduring,
   unequable, unequal, uneven, unfixed, unforeseeable, ungraded,
   unguarded, unjoined, unmethodical, unmetrical, unordered,
   unorganized, unorthodox, unpersuaded, unpredictable, unprovable,
   unreasonable, unreasoning, unreflecting, unregular, unreliable,
   unresolved, unrestrained, unrhythmical, unsettled, unsorted,
   unstable, unstable as water, unstaid, unsteadfast, unsteady,
   unsure, unsymmetrical, unsystematic, unthinking, unthoughtful,
   ununiform, unverifiable, vacillating, vagarious, vagrant, vague,
   variable, variegated, variform, various, varying, veering,
   vicissitudinary, vicissitudinous, volatile, wandering, wanton,
   wavering, wavery, wavy, wayward, whimsical, wishy-washy, wobbling,
   wobbly