The Collaborative International Dictionary of English v.0.48:

Difficulty \Dif"fi*cul*ty\, n.; pl. Difficulties. [L.
   difficultas, fr. difficilis difficult; dif- = dis- + facilis
   easy: cf. F. difficult['e]. See Facile.]
   1. The state of being difficult, or hard to do; hardness;
      arduousness; -- opposed to easiness or facility; as,
      the difficulty of a task or enterprise; a work of
      difficulty.
      [1913 Webster]

            Not being able to promote them [the interests of
            life] on account of the difficulty of the region.
                                                  --James Byrne.
      [1913 Webster]

   2. Something difficult; a thing hard to do or to understand;
      that which occasions labor or perplexity, and requires
      skill and perseverance to overcome, solve, or achieve; a
      hard enterprise; an obstacle; an impediment; as, the
      difficulties of a science; difficulties in theology.
      [1913 Webster]

            They lie under some difficulties by reason of the
            emperor's displeasure.                --Addison.
      [1913 Webster]

   3. A controversy; a falling out; a disagreement; an
      objection; a cavil.
      [1913 Webster]

            Measures for terminating all local difficulties.
                                                  --Bancroft.
      [1913 Webster]

   4. Embarrassment of affairs, especially financial affairs; --
      usually in the plural; as, to be in difficulties.
      [1913 Webster]

            In days of difficulty and pressure.   --Tennyson.

   Syn: Impediment; obstacle; obstruction; embarrassment;
        perplexity; exigency; distress; trouble; trial;
        objection; cavil. See Impediment.
        [1913 Webster]

WordNet (r) 3.0 (2006):

difficulty
    n 1: an effort that is inconvenient; "I went to a lot of
         trouble"; "he won without any trouble"; "had difficulty
         walking"; "finished the test only with great difficulty"
         [syn: trouble, difficulty]
    2: a factor causing trouble in achieving a positive result or
       tending to produce a negative result; "serious difficulties
       were encountered in obtaining a pure reagent"
    3: a condition or state of affairs almost beyond one's ability
       to deal with and requiring great effort to bear or overcome;
       "grappling with financial difficulties"
    4: the quality of being difficult; "they agreed about the
       difficulty of the climb" [syn: difficulty, difficultness]
       [ant: ease, easiness, simpleness, simplicity]

Moby Thesaurus II by Grady Ward, 1.0:

168 Moby Thesaurus words for "difficulty":
   Gordian knot, abstruseness, adverse circumstances, adversity,
   affliction, aggravation, agreement to disagree, altercation,
   annoyance, arduousness, asperity, bad news, bedevilment, beef,
   bickering, blight, block, blockade, bore, bother, botheration,
   bothersomeness, bottleneck, bummer, burden, burthen, care, cargo,
   catch, challenge, charge, complexity, complication, controversy,
   cordon, crabbedness, crampedness, crashing bore, cross,
   cross-purposes, cumbrance, curse, curtain, deadweight, deepness,
   demurral, demurrer, determent, deterrent, devilment, difference,
   difference of opinion, difficulties, dilemma, disadvantage,
   disagreement, disparity, dispute, distress, dividedness, division,
   dogging, downer, drag, drawback, embarrassment, emergency,
   encumbrance, esoterica, exasperation, exigency, falling-out, fight,
   fix, formidableness, freight, hamper, handicap, hang-up,
   harassment, hard knocks, hard life, hard lot, hardcase, hardness,
   hardship, harrying, hassle, hazard, headache, heavy sledding,
   hindrance, hitch, hot water, hounding, hurdle, impediment,
   impedimenta, imposition, inconvenience, intricacy, irritation, jam,
   joker, knottiness, laboriousness, load, lumber, mess,
   misunderstanding, molestation, nuisance, objection, obstacle,
   obstruction, obstructive, odds, one small difficulty, onus, pack,
   painfulness, pass, penalty, persecution, pest, pickle, pinch,
   pitfall, plight, polarization, predicament, pressure, problem,
   profoundness, profundity, protest, quandary, question,
   reconditeness, remonstrance, remonstration, rigor, rub, scrape,
   sea of troubles, snag, squabble, strain, strait, straits, stress,
   stress of life, stumbling block, stumbling stone, trial,
   tribulation, trouble, troubles, vale of tears, variance, vexation,
   vexatiousness, vicissitude, vigor, weight, white elephant,
   worriment, worry