The Collaborative International Dictionary of English v.0.48:

Fitful \Fit"ful\, a. [From 7th Fit.]
   Full of fits; irregularly variable; impulsive and unstable.
   [1913 Webster]

         After life's fitful fever, he sleeps well. --Shak.
   -- Fit"ful*ly, adv. -- Fit"ful*ness, n.
   [1913 Webster]

         The victorious trumpet peal
         Dies fitfully away.                      --Macaulay.
   Fithel

WordNet (r) 3.0 (2006):

fitful
    adj 1: occurring in spells and often abruptly; "fitful bursts of
           energy"; "spasmodic rifle fire" [syn: fitful,
           spasmodic]
    2: intermittently stopping and starting; "fitful (or
       interrupted) sleep"; "off-and-on static" [syn: fitful,
       interrupted, off-and-on(a)]

Moby Thesaurus II by Grady Ward, 1.0:

189 Moby Thesaurus words for "fitful":
   adrift, afloat, aimless, alternating, amorphous, broken,
   broken off, capricious, careening, casual, catchy, changeable,
   changeful, chopped-off, choppy, convulsive, correctly, decently,
   decorously, decousu, desultory, deviable, deviative,
   disarticulated, disconnected, discontinued, discontinuous,
   discrete, disjunct, disjunctive, disordered, dispersed,
   disproportionate, dizzy, eccentric, eclamptic, episodic, erratic,
   fast and loose, fickle, fidgety, fitly, fittingly, flickering,
   flighty, flitting, fluctuating, formless, freakish, frivolous,
   giddy, gratuitous, guttering, halting, haphazard, herky-jerky,
   heteroclite, hit-or-miss, immethodical, impetuous, impulsive,
   inchoate, incoherent, inconsistent, inconstant, indecisive,
   indiscriminate, infirm, intermittent, intermitting, interrupted,
   irregular, irresolute, irresponsible, jagged, jerking, jerky,
   jiggety, jumpy, justly, lurching, mazy, meaningless, mercurial,
   misshapen, moody, nicely, noncontinuous, nonlinear, nonsequential,
   nonserial, nonsymmetrical, nonsystematic, nonuniform, occasional,
   on-again-off-again, orderless, orgasmic, parenthetic, patchy,
   periodic, planless, promiscuous, properly, rambling, random,
   recurrent, restless, rightly, rough, roving, saltatory,
   scatterbrained, scrappy, senseless, shapeless, shifting, shifty,
   shuffling, snatchy, spasmatic, spasmic, spasmodic, spastic,
   spineless, sporadic, spotty, staggering, straggling, straggly,
   suspended, systemless, twitchety, twitching, twitchy,
   unaccountable, unarranged, uncertain, unclassified, unconnected,
   uncontrolled, undependable, undirected, undisciplined, unequal,
   uneven, unfixed, ungraded, unjoined, unmethodical, unmetrical,
   unordered, unorganized, unpredictable, unregular, unreliable,
   unrestrained, unrhythmical, unsettled, unsorted, unstable,
   unstable as water, unstaid, unsteadfast, unsteady, unsuccessive,
   unsymmetrical, unsystematic, ununiform, vacillating, vagrant,
   vague, variable, varying, veering, vellicative, vicissitudinary,
   vicissitudinous, volatile, wandering, wanton, wavering, wavery,
   wavy, wayward, whimsical, wishy-washy, wobbling, wobbly