The Collaborative International Dictionary of English v.0.48:

Anxiety \Anx*i"e*ty\, n.; pl. Anxieties. [L. anxietas, fr.
   anxius: cf. F. anxi['e]t['e]. See Anxious.]
   1. Concern or solicitude respecting some thing or event,
      future or uncertain, which disturbs the mind, and keeps it
      in a state of painful uneasiness.
      [1913 Webster]

   2. Eager desire. --J. D. Forbes
      [1913 Webster]

   3. (Med.) A state of restlessness and agitation, often with
      general indisposition and a distressing sense of
      oppression at the epigastrium. --Dunglison.
      [1913 Webster]

   Syn: Care; solicitude; foreboding; uneasiness; perplexity;
        disquietude; disquiet; trouble; apprehension;
        restlessness. See Care.
        [1913 Webster]

WordNet (r) 3.0 (2006):

anxiety
    n 1: (psychiatry) a relatively permanent state of worry and
         nervousness occurring in a variety of mental disorders,
         usually accompanied by compulsive behavior or attacks of
         panic [syn: anxiety, anxiousness]
    2: a vague unpleasant emotion that is experienced in
       anticipation of some (usually ill-defined) misfortune

Moby Thesaurus II by Grady Ward, 1.0:

159 Moby Thesaurus words for "anxiety":
   abstraction, abulia, ache, ado, alacrity, alienation, all-overs,
   angst, anguish, animation, annoyance, anxiety equivalent,
   anxiety state, anxiousness, apathy, appetite, apprehension,
   apprehensiveness, avidity, avidness, besetment, boredom, bother,
   breathless impatience, can of worms, catatonic stupor, chafing,
   cheerful readiness, cheerlessness, cliff-hanging, compulsion,
   concern, concernment, dejection, depression, desire, detachment,
   disadvantage, discomfort, discomposure, discontent, dislike,
   displeasure, disquiet, disquietude, dissatisfaction, distress,
   doubt, dread, dullness, eagerness, elan, elation, emotionalism,
   emptiness, ennui, euphoria, evil, excitement, existential woe,
   expectant waiting, flatness, folie du doute, foreboding,
   forwardness, fretfulness, fretting, great ado, grimness, gust,
   gusto, haste, headache, hypochondria, hysteria, hysterics,
   impatience, impatientness, impetuousness, inconvenience,
   indifference, inquietude, insensibility, joylessness, keen desire,
   keenness, lack of pleasure, lather, lethargy, life, liveliness,
   longing, malaise, mania, matter, melancholia, mental distress,
   misery, misgiving, mistrust, nausea, nervousness, nongratification,
   nonsatisfaction, obsession, painfulness, panic,
   pathological indecisiveness, peck of troubles, pessimism,
   preoccupation, problem, promptness, psychalgia,
   psychomotor disturbance, qualm, qualmishness, quickness, readiness,
   restiveness, restlessness, savorlessness, sea of troubles,
   solicitude, spirit, spleen, staleness, stew, stupor, suffering,
   suspense, sweat, tastelessness, tediousness, tedium,
   tense readiness, thirst, tic, trouble, twitching, uncertainty,
   uncomfortableness, unease, uneasiness, unhappiness, unpatientness,
   unpleasure, unquietness, unresponsiveness, unsatisfaction, verve,
   vexation of spirit, vitality, vivacity, waiting, withdrawal, worry,
   zest, zestfulness