The Collaborative International Dictionary of English v.0.48:

Annoyance \An*noy"ance\, n. [OF. anoiance, anuiance.]
   1. The act of annoying, or the state of being annoyed;
      molestation; vexation; annoy.
      [1913 Webster]

            A deep clay, giving much annoyance to passengers.
                                                  --Fuller.
      [1913 Webster]

            For the further annoyance and terror of any besieged
            place, they would throw into it dead bodies.
                                                  --Wilkins.
      [1913 Webster]

   2. That which annoys.
      [1913 Webster]

            A grain, a dust, a gnat, a wandering hair,
            Any annoyance in that precious sense. --Shak.
      [1913 Webster]

WordNet (r) 3.0 (2006):

annoyance
    n 1: the psychological state of being irritated or annoyed [syn:
         irritation, annoyance, vexation, botheration]
    2: anger produced by some annoying irritation [syn: annoyance,
       chafe, vexation]
    3: an unpleasant person who is annoying or exasperating [syn:
       aggravator, annoyance]
    4: something or someone that causes trouble; a source of
       unhappiness; "washing dishes was a nuisance before we got a
       dish washer"; "a bit of a bother"; "he's not a friend, he's
       an infliction" [syn: annoyance, bother, botheration,
       pain, infliction, pain in the neck, pain in the ass]
    5: the act of troubling or annoying someone [syn: annoyance,
       annoying, irritation, vexation]

Moby Thesaurus II by Grady Ward, 1.0:

126 Moby Thesaurus words for "annoyance":
   ado, adverse circumstances, adversity, affliction, aggravation,
   amplification, anger, annoyingness, anxiety, augmentation,
   aversion, bad news, bedevilment, besetment, blight, bore, bother,
   botheration, bothering, bothersomeness, bummer, can of worms, care,
   contentiousness, crashing bore, cross, curse, deepening,
   deliberate aggravation, deterioration, devilment, difficulties,
   difficulty, disadvantage, disapprobation, disapproval, discontent,
   disgust, dislike, displeasure, dissatisfaction, distaste, distress,
   dogging, downer, drag, embittering, embitterment, enhancement,
   enlargement, evil, exacerbation, exasperation, great ado,
   harassment, hard knocks, hard life, hard lot, hardcase, hardship,
   harrying, headache, heightening, hounding, inconvenience, increase,
   indignation, intensification, ire, irking, irksomeness, irritant,
   irritation, magnification, matter, molestation, nuisance, pain,
   peck of troubles, persecution, peskiness, pest, pester, pestering,
   pestiferousness, pique, plague, plaguesomeness, plight, pother,
   predicament, pressure, problem, provocation, provoking,
   provokingness, repugnance, repulsion, resentfulness, resentment,
   revulsion, riding, rigor, sea of troubles, sharpening, souring,
   stress, stress of life, teasing, tiresomeness, trial, tribulation,
   trouble, troubles, troublesomeness, vale of tears, vexation,
   vexatiousness, vexing, vicissitude, wearisomeness, worriment,
   worrisomeness, worry, worsening, wrath