The Collaborative International Dictionary of English v.0.48:

irritated \irritated\ adj.
   aroused to impatience or anger; as, made an irritated
   gesture.

   Syn: annoyed, nettled, peeved, pissed, stung.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Irritate \Ir"ri*tate\, v. t. [imp. & p. p. Irritated; p. pr. &
   vb. n. Irritating.] [L. irritatus, p. p. of irritare. Of
   doubtful origin.]
   [1913 Webster]
   1. To increase the action or violence of; to heighten
      excitement in; to intensify; to stimulate.
      [1913 Webster]

            Cold maketh the spirits vigorous and irritateth
            them.                                 --Bacon.
      [1913 Webster]

   2. To excite anger or displeasure in; to provoke; to tease;
      to exasperate; to annoy; to vex; as, the insolence of a
      tyrant irritates his subjects.
      [1913 Webster]

            Dismiss the man, nor irritate the god:
            Prevent the rage of him who reigns above. --Pope.
      [1913 Webster]

   3. (Physiol.) To produce irritation in; to stimulate; to
      cause to contract. See Irritation, n., 2.
      [1913 Webster]

   4. (Med.) To make morbidly excitable, or oversensitive; to
      fret; as, the skin is irritated by friction; to irritate a
      wound by a coarse bandage.

   Syn: To fret; inflame; excite; provoke; tease; vex;
        exasperate; anger; incense; enrage.

   Usage: To Irritate, Provoke, Exasperate. These words
          express different stages of excited or angry feeling.
          Irritate denotes an excitement of quick and slightly
          angry feeling which is only momentary; as, irritated
          by a hasty remark. To provoke implies the awakening of
          some open expression of decided anger; as, a provoking
          insult. Exasperate denotes a provoking of anger at
          something unendurable. Whatever comes across our
          feelings irritates; whatever excites anger provokes;
          whatever raises anger to a high point exasperates.
          "Susceptible and nervous people are most easily
          irritated; proud people are quickly provoked; hot and
          fiery people are soonest exasperated." --Crabb.
          [1913 Webster]

WordNet (r) 3.0 (2006):

irritated
    adj 1: aroused to impatience or anger; "made an irritated
           gesture"; "feeling nettled from the constant teasing";
           "peeved about being left out"; "felt really pissed at her
           snootiness"; "riled no end by his lies"; "roiled by the
           delay" [syn: annoyed, irritated, miffed, nettled,
           peeved, pissed, pissed off, riled, roiled,
           steamed, stung]

Moby Thesaurus II by Grady Ward, 1.0:

91 Moby Thesaurus words for "irritated":
   aggravated, algetic, amplified, angry, annoyed, augmented,
   bothered, broken, browned-off, bugged, burned, burning, burnt-up,
   burst, busted, chafed, checked, chipped, cracked, crazed, cut,
   damaged, deliberately provoked, deteriorated, disturbed,
   embittered, enhanced, enlarged, exacerbated, exasperated,
   festering, fiery, galled, griped, harmed, heated up, heightened,
   hotted up, huffy, hurt, impaired, imperfect, in bits, in pieces,
   in shards, increased, inflamed, injured, intensified, irked,
   lacerated, magnified, mangled, miffed, mutilated, nettled, peeved,
   piqued, provoked, put-out, rankling, raw, red, rent, resentful,
   riled, roiled, ruffled, ruptured, scalded, scorched, sensitive,
   shattered, slashed, slit, smarting, smashed, sore, soured, split,
   sprung, tender, the worse for, tingling, torn, troubled, vexed,
   weakened, worse, worse off, worsened