The Collaborative International Dictionary of English v.0.48:

Petulant \Pet"u*lant\, a. [L. petulans, -antis, prop., making
   slight attacks upon, from a lost dim. of petere to fall upon,
   to attack: cf. F. p['e]tulant. See Petition.]
   1. Forward; pert; insolent; wanton. [Obs.] --Burton.
      [1913 Webster]

   2. Capriciously fretful; characterized by ill-natured
      freakishness; irritable. "Petulant moods." --Macaulay.
      [1913 Webster]

   Syn: Irritable; ill-humored; peevish; cross; fretful;
        querulous.
        [1913 Webster]

WordNet (r) 3.0 (2006):

petulant
    adj 1: easily irritated or annoyed; "an incorrigibly fractious
           young man"; "not the least nettlesome of his countrymen"
           [syn: cranky, fractious, irritable, nettlesome,
           peevish, peckish, pettish, petulant, scratchy,
           testy, tetchy, techy]

Moby Thesaurus II by Grady Ward, 1.0:

109 Moby Thesaurus words for "petulant":
   Jeremianic, arbitrary, bad-tempered, beefing, bellyaching, bilious,
   bitching, cantankerous, capricious, captious, catty, choleric,
   complaining, complaintful, crabbed, crabbing, crabby, cranky,
   croaking, cross, crotchety, disappointed, discontented,
   disgruntled, displeased, dissatisfied, envious, fanciful,
   fantasied, fantastic, faultfinding, flaky, fractious, freakish,
   fretful, griping, grouchy, grousing, growling, grumbling, grumpy,
   harebrained, howling, huffish, huffy, humorsome, ill-humored,
   ill-tempered, impatient, irascible, irritable, kinky, lamentive,
   maggoty, malcontent, malcontented, moanful, moody, motiveless,
   mournful, murmuring, muttering, nagging, naggy, notional,
   out of humor, peevish, perverse, pettish, plaintive, plangent,
   puling, querulant, querulous, quirky, rebellious, resentful,
   restive, restless, shrewish, snappish, sorrowful, sour, splenetic,
   sulky, temperamental, testy, ululant, unaccepting, unaccommodating,
   uneasy, unfulfilled, ungratified, unhappy, unreasonable,
   unrestrained, unsatisfied, vagarious, vagrant, vixenish, vixenly,
   wailful, wanton, waspish, wayward, whimpering, whimsical, whining,
   whiny