The Collaborative International Dictionary of English v.0.48:

Vacillate \Vac"il*late\ (v[a^]s"[i^]l*l[=a]t), v. i. [imp. & p.
   p. Vacillated (v[a^]s"[i^]l*l[=a]`t[e^]d); p. pr. & vb. n.
   Vacillating.] [L. vacillare, vacillatum; cf. Skr. va[~n]c.]
   [1913 Webster]
   1. To move one way and the other; to reel or stagger; to
      waver.
      [1913 Webster]

            [A spheroid] is always liable to shift and
            vacillatefrom one axis to another.    --Paley.
      [1913 Webster]

   2. To fluctuate in mind or opinion; to be unsteady or
      inconstant; to waver.
      [1913 Webster]

   Syn: See Fluctuate.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Vacillating \Vac"il*la`ting\, a.
   Inclined to fluctuate; wavering. --Tennyson. --
   Vac"il*la`ting*ly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

vacillating
    adj 1: uncertain in purpose or action [syn: vacillant,
           vacillating, wavering]

Moby Thesaurus II by Grady Ward, 1.0:

98 Moby Thesaurus words for "vacillating":
   adrift, afloat, alternating, amorphous, capricious, changeable,
   changeful, coquettish, desultory, deviable, dizzy, eccentric,
   erratic, faddish, fast and loose, fickle, fitful, flickering,
   flighty, flirtatious, flitting, fluctuant, fluctuating,
   fluctuational, freakish, giddy, harmonic, impetuous, impulsive,
   inconsistent, inconstant, indecisive, infirm, irregular,
   irresolute, irresponsible, libratory, light, mazy, mercurial,
   moody, nutational, oscillating, oscillatory, pendular, pendulating,
   pendulous, periodic, quicksilver, rambling, resonant, restless,
   roving, scatterbrained, shapeless, shifting, shifty, shilly-shally,
   shilly-shallying, shuffling, skittish, spasmodic, spineless,
   toying, unaccountable, uncertain, uncontrolled, undependable,
   undisciplined, unfixed, unpredictable, unreliable, unrestrained,
   unsettled, unstable, unstable as water, unstaid, unsteadfast,
   unsteady, vacillatory, vagrant, variable, versatile, vibratile,
   vibrating, vibratory, vicissitudinary, vicissitudinous, volatile,
   wandering, wanton, wavering, wavery, wavy, wayward, whimsical,
   wishy-washy, wobbly