The Collaborative International Dictionary of English v.0.48:

Skittish \Skit"tish\, a. [See Skit, v. t.]
   1. Easily frightened; timorous; shy; untrustworthy; as, a
      skittish colt. "A restiff, skittish jade." --L'Estrange.
      [1913 Webster]

   2. Wanton; restive; freakish; volatile; changeable; fickle.
      "Skittish Fortune's hall." --Shak.
      [1913 Webster] -- Skit"tish*ly, adv. --
      Skit"tish*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

skittish
    adj 1: unpredictably excitable (especially of horses) [syn:
           skittish, flighty, spooky, nervous]

Moby Thesaurus II by Grady Ward, 1.0:

128 Moby Thesaurus words for "skittish":
   agitable, allergic, anaphylactic, animated, antic, bashful,
   capersome, changeable, coltish, combustible, confused, conscious,
   coquettish, cowardly, coy, delicate, demure, diffident, dizzy,
   edgy, emotional, emotionally unstable, empathetic, empathic,
   empty-headed, eruptive, excitable, explosive, exuberant, faddish,
   fearful, fearing, fearsome, fickle, flighty, flirtatious, frisky,
   frivolous, frolicsome, full of beans, gamesome, gay, giddy, goosy,
   harebrained, hearty, high-mettled, high-spirited, high-strung,
   highly emotional, hyperesthetic, hyperpathic, hypersensitive,
   in fear, inarticulate, inconstant, inflammable, irascible,
   irresponsible, irritable, itchy, jumpy, light, light-headed,
   lively, mercurial, mettlesome, mousy, nervous, overrefined,
   oversensible, oversensitive, overtender, passible, perturbable,
   playful, prickly, quicksilver, rabbity, rattlebrained, refined,
   responsive, restive, rollicking, rollicksome, rompish, scary,
   scatterbrained, self-conscious, sensitive, shaky, shamefaced,
   shamefast, shivery, shrinking, shy, skittery, spirited, sportive,
   sprightly, stammering, startlish, supersensitive, sympathetic,
   tactful, tender, tetchy, thin-skinned, ticklish, timid, timorous,
   touchy, toying, trembling, tremulous, trepidant, trigger-happy,
   undependable, unpredictable, unreliable, vacillating, versatile,
   vital, vivacious, volatile, volcanic, zestful, zippy