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]