The Collaborative International Dictionary of English v.0.48:

pain \pain\ (p[=a]n), n. [OE. peine, F. peine, fr. L. poena,
   penalty, punishment, torment, pain; akin to Gr. poinh`
   penalty. Cf. Penal, Pine to languish, Punish.]
   1. Punishment suffered or denounced; suffering or evil
      inflicted as a punishment for crime, or connected with the
      commission of a crime; penalty. --Chaucer.
      [1913 Webster]

            We will, by way of mulct or pain, lay it upon him.
                                                  --Bacon.
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            Interpose, on pain of my displeasure. --Dryden.
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            None shall presume to fly, under pain of death.
                                                  --Addison.
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   2. Any uneasy sensation in animal bodies, from slight
      uneasiness to extreme distress or torture, proceeding from
      a derangement of functions, disease, or injury by
      violence; bodily distress; bodily suffering; an ache; a
      smart. "The pain of Jesus Christ." --Chaucer.
      [1913 Webster]

   Note: Pain may occur in any part of the body where sensory
         nerves are distributed, and it is always due to some
         kind of stimulation of them. The sensation is generally
         interpreted as originating at the peripheral end of the
         nerve.
         [1913 Webster]

   3. pl. Specifically, the throes or travail of childbirth.
      [1913 Webster]

            She bowed herself and travailed, for her pains came
            upon her.                             --1 Sam. iv.
                                                  19.
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   4. Uneasiness of mind; mental distress; disquietude; anxiety;
      grief; solicitude; anguish. Also called mental pain.
      --Chaucer.
      [1913 Webster +PJC]

            In rapture as in pain.                --Keble.
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   5. See Pains, labor, effort.
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   Bill of pains and penalties. See under Bill.

   To die in the pain, to be tortured to death. [Obs.]
      --Chaucer.
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The Collaborative International Dictionary of English v.0.48:

Pain \Pain\, v. t. [imp. & p. p. Pained (p[=a]nd); p. pr. &
   vb. n. Paining.] [OE. peinen, OF. pener, F. peiner to
   fatigue. See Pain, n.]
   1. To inflict suffering upon as a penalty; to punish. [Obs.]
      --Wyclif (Acts xxii. 5).
      [1913 Webster]

   2. To put to bodily uneasiness or anguish; to afflict with
      uneasy sensations of any degree of intensity; to torment;
      to torture; as, his dinner or his wound pained him; his
      stomach pained him.
      [1913 Webster]

            Excess of cold, as well as heat, pains us. --Locke
      .
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   3. To render uneasy in mind; to disquiet; to distress; to
      grieve; as, a child's faults pain his parents.
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            I am pained at my very heart.         --Jer. iv. 19.
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   To pain one's self, to exert or trouble one's self; to take
      pains; to be solicitous. [Obs.] "She pained her to do all
      that she might." --Chaucer.
      [1913 Webster]

   Syn: To disquiet; trouble; afflict; grieve; aggrieve;
        distress; agonize; torment; torture.
        [1913 Webster]

WordNet (r) 3.0 (2006):

pain
    n 1: a symptom of some physical hurt or disorder; "the patient
         developed severe pain and distension" [syn: pain,
         hurting]
    2: emotional distress; a fundamental feeling that people try to
       avoid; "the pain of loneliness" [syn: pain, painfulness]
       [ant: pleasance, pleasure]
    3: a somatic sensation of acute discomfort; "as the intensity
       increased the sensation changed from tickle to pain" [syn:
       pain, pain sensation, painful sensation]
    4: a bothersome annoying person; "that kid is a terrible pain"
       [syn: pain, pain in the neck, nuisance]
    5: 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]
    v 1: cause bodily suffering to and make sick or indisposed [syn:
         trouble, ail, pain]
    2: cause emotional anguish or make miserable; "It pains me to
       see my children not being taught well in school" [syn:
       pain, anguish, hurt]

Moby Thesaurus II by Grady Ward, 1.0:

248 Moby Thesaurus words for "pain":
   abscess, ache, aching, afflict, affliction, aggrieve, agonize,
   agony, ague, ail, anemia, anguish, ankylosis, annoyance, anoxia,
   apnea, asphyxiation, assiduousness, asthma, ataxia, atrophy,
   backache, barb the dart, bite, bitterness, bleakness, bleeding,
   blennorhea, blow, bore, bother, bruise, burn, cachexia, cachexy,
   castigation, chafe, chastening, chastisement, cheerlessness, chill,
   chills, colic, comfortlessness, condign punishment, constipation,
   constrain, convulse, convulsion, correction, coughing, cramp,
   crucify, cut, cut up, cyanosis, depress, depression, deserts,
   despair, diarrhea, diligence, disciplinary measures, discipline,
   discomfort, discomposure, dismalness, dismay, disquiet, distress,
   distressfulness, dizziness, dolor, drag, dreariness, dropsy,
   dysentery, dyspepsia, dyspnea, edema, effort, elbow grease,
   emaciation, excruciate, exertion, fainting, fatigue, ferule,
   fester, fever, fibrillation, flux, fret, gall, give pain, gnaw,
   grate, grief, grieve, grievousness, grind, gripe, growth, harass,
   harrow, headache, hemorrhage, high blood pressure, hurt,
   hurt the feelings, hydrops, hypertension, hypotension, icterus,
   indigestion, industry, inflame, inflammation, inflict pain,
   infliction, injure, injury, insomnia, irk, irritate, irritation,
   itching, jaundice, joylessness, judgment, judicial punishment,
   kill by inches, labor, labored breathing, lacerate, lament,
   lamentability, lamentation, lesion, low blood pressure, lumbago,
   marasmus, martyr, martyrize, misery, mourn, mournfulness,
   nasal discharge, nasty blow, nausea, necrosis, nemesis, nip,
   nuisance, ordeal, painfulness, pains, pains and punishments, pang,
   paralysis, passion, pathos, pay, payment, penal retribution,
   penalty, penology, pest, pierce, pinch, pitiability, pitiableness,
   pitifulness, poignancy, prick, prolong the agony, pruritus,
   punishment, punition, put to torture, rack, rankle, rash, rasp,
   regrettableness, retribution, retributive justice, rheum, rub,
   sadden, sadness, sclerosis, scourge, sedulousness, seizure,
   sharpness, shock, skin eruption, smarting, sneezing, sore,
   sore spot, soreness, sorrow, sorrowfulness, spasm, stab, sting,
   stitch, strain, stress, stress of life, stroke, suffer, suffering,
   tabes, tachycardia, tender spot, throes, toil, torment, torture,
   travail, trial, tribulation, trouble, try, tumor, tweak, twinge,
   twist, twist the knife, upset, upset stomach, vertigo, vexation,
   vomiting, wasting, well-deserved punishment, what-for, while, woe,
   woebegoneness, woefulness, wound, wrench, wretchedness, wring



The Devil's Dictionary (1881-1906):

PAIN, n.  An uncomfortable frame of mind that may have a physical
basis in something that is being done to the body, or may be purely
mental, caused by the good fortune of another.