The Collaborative International Dictionary of English v.0.48:

Sympathy \Sym"pa*thy\, n.; pl. Sympathies. [F. sympathie, L.
   sympathia, Gr. ?; sy`n with + ? suffering, passion, fr. ?, ?,
   to suffer. See Syn-, and Pathos.]
   1. Feeling corresponding to that which another feels; the
      quality of being affected by the affection of another,
      with feelings correspondent in kind, if not in degree;
      fellow-feeling.
      [1913 Webster]

            They saw, but other sight instead -- a crowd
            Of ugly serpents! Horror on them fell,
            And horrid sympathy.                  --Milton.
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   2. An agreement of affections or inclinations, or a
      conformity of natural temperament, which causes persons to
      be pleased, or in accord, with one another; as, there is
      perfect sympathy between them.
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   3. Kindness of feeling toward one who suffers; pity;
      commiseration; compassion.
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            I value myself upon sympathy, I hate and despise
            myself for envy.                      --Kames.
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   4. (Physiol. & Med.)
      (a) The reciprocal influence exercised by organs or parts
          on one another, as shown in the effects of a diseased
          condition of one part on another part or organ, as in
          the vomiting produced by a tumor of the brain.
      (b) The influence of a certain psychological state in one
          person in producing a like state in another.

   Note: In the original 1890 work, sense (b) was described as:
         "That relation which exists between different persons
         by which one of them produces in the others a state or
         condition like that of himself. This is shown in the
         tendency to yawn which a person often feels on seeing
         another yawn, or the strong inclination to become
         hysteric experienced by many women on seeing another
         person suffering with hysteria."
         [Webster 1913 Suppl. +PJC]

   5. A tendency of inanimate things to unite, or to act on each
      other; as, the sympathy between the loadstone and iron.
      [R.]
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   6. Similarity of function, use office, or the like.
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            The adverb has most sympathy with the verb. --Earle.
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   Syn: Pity; fellow-feeling; compassion; commiseration;
        tenderness; condolence; agreement.

   Usage: Sympathy, Commiseration. Sympathy is literally a
          fellow-feeling with others in their varied conditions
          of joy or of grief. This term, however, is now more
          commonly applied to a fellow-feeling with others under
          affliction, and then coincides very nearly with
          commiseration. In this case it is commonly followed by
          for; as, to feel sympathy for a friend when we see him
          distressed. The verb sympathize is followed by with;
          as, to sympathize with a friend in his distresses or
          enjoyments. "Every man would be a distinct species to
          himself, were there no sympathy among individuals."
          --South. See Pity.
          [1913 Webster]

                Fault,
                Acknowledged and deplored, in Adam wrought
                Commiseration.                    --Milton.
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WordNet (r) 3.0 (2006):

sympathy
    n 1: an inclination to support or be loyal to or to agree with
         an opinion; "his sympathies were always with the underdog";
         "I knew I could count on his understanding" [syn:
         sympathy, understanding]
    2: sharing the feelings of others (especially feelings of sorrow
       or anguish) [syn: sympathy, fellow feeling]
    3: a relation of affinity or harmony between people; whatever
       affects one correspondingly affects the other; "the two of
       them were in close sympathy"

Moby Thesaurus II by Grady Ward, 1.0:

272 Moby Thesaurus words for "sympathy":
   abetment, accord, accordance, addition, adduction, adjunct,
   advocacy, aegis, affairs, affectionateness, affections,
   affective faculty, affectivity, affiliation, affinity, agape,
   agreement, aid and comfort, allergy, alliance, allurement, amity,
   an in, anaphylaxis, approximation, assemblage, association,
   assurance, attractance, attraction, attractiveness, attractivity,
   auspices, backing, balm, benevolence, benignancy, benignity, bent,
   bias, blending, bond, bonds of harmony, brotherhood,
   brotherly love, camaraderie, capillarity, capillary attraction,
   care, caring, caritas, cement of friendship, centripetal force,
   championship, charity, chiming, chord, clemency, closeness,
   combination, comfort, commiseration, communion, community,
   community of interests, compassion, compatibility, concern,
   concord, concordance, condolement, condolence, congeniality,
   connectedness, connection, considerateness, consolation, consonant,
   contiguity, contrariety, correspondence, countenance, dealings,
   deduction, delicacy, disjunction, drag, draw, easement, echo,
   emotional life, emotions, empathy, encouragement, esprit,
   esprit de corps, exquisiteness, fancy, fascination, favor,
   favorable regard, feeling, feeling of identity, feeling of kinship,
   feeling tone, feelings, fellow feeling, fellowship, filiation,
   fineness, finer feelings, forbearance, forgiveness, fosterage,
   fraternal feeling, frictionlessness, friendly relations,
   good graces, good terms, good understanding, good vibes,
   good vibrations, goodness, goodness of heart, goodwill, grace,
   graciousness, gravitation, gravity, guidance, happy family,
   harmonic, harmony, heart, heart of gold, homology, humaneness,
   humanity, hyperesthesia, hyperpathia, hypersensitivity,
   identification, identity, inclination, intercourse, interest,
   intimacy, involvement, irritability, junction, kindheartedness,
   kindliness, kindly disposition, kindness, kinship, leaning,
   leniency, liaison, like-mindedness, link, linkage, linking, love,
   loving kindness, magnetism, mercy, mitigation, musical,
   mutual affinity, mutual attraction, mutual regard, mutuality,
   nearness, nervousness, niceness, oneness, oversensibility,
   oversensitiveness, overtenderness, pardon, partiality, passibility,
   passions, pathos, patronage, peace, penchant, perceptiveness,
   perceptivity, photophobia, pity, predilection, preference,
   prickliness, proclivity, propensity, propinquity, proximity, pull,
   pulling power, quarter, rapport, rapprochement, reassurance,
   reciprocity, regard, relatedness, relating, relation, relations,
   relationship, relief, reprieve, respect, response, responsiveness,
   rue, ruth, seconding, self-pity, sensibilities, sensitiveness,
   sensitivity, sensitization, sentiments, sharing, sharing of grief,
   shred of comfort, similarity, softheartedness, solace, solacement,
   solicitousness, solidarity, soothing words, soreness,
   soul of kindness, sponsorship, supersensitivity, support,
   susceptibilities, sympathetic chord, sympathetic response,
   sympathies, symphonic, symphonious, symphony, tact, tactfulness,
   team spirit, tender susceptibilities, tenderheartedness,
   tenderness, tetchiness, thin skin, ticklishness, tie, tie-in,
   touchiness, traction, tug, turn, tutelage, understanding, union,
   unison, unity, vibes, vibrations, warmheartedness, warmth,
   warmth of heart