The Collaborative International Dictionary of English v.0.48:

Die \Die\, v. i. [imp. & p. p. Died; p. pr. & vb. n. Dying.]
   [OE. deyen, dien, of Scand. origin; cf. Icel. deyja; akin to
   Dan. d["o]e, Sw. d["o], Goth. diwan (cf. Goth. afd?jan to
   harass), OFries. d?ia to kill, OS. doian to die, OHG. touwen,
   OSlav. daviti to choke, Lith. dovyti to torment. Cf. Dead,
   Death.]
   1. To pass from an animate to a lifeless state; to cease to
      live; to suffer a total and irreparable loss of action of
      the vital functions; to become dead; to expire; to perish;
      -- said of animals and vegetables; often with of, by,
      with, from, and rarely for, before the cause or occasion
      of death; as, to die of disease or hardships; to die by
      fire or the sword; to die with horror at the thought.
      [1913 Webster]

            To die by the roadside of grief and hunger.
                                                  --Macaulay.
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            She will die from want of care.       --Tennyson.
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   2. To suffer death; to lose life.
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            In due time Christ died for the ungodly. --Rom. v.
                                                  6.
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   3. To perish in any manner; to cease; to become lost or
      extinct; to be extinguished.
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            Letting the secret die within his own breast.
                                                  --Spectator.
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            Great deeds can not die.              --Tennyson.
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   4. To sink; to faint; to pine; to languish, with weakness,
      discouragement, love, etc.
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            His heart died within, and he became as a stone. --1
                                                  Sam. xxv. 37.
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            The young men acknowledged, in love letters, that
            they died for Rebecca.                --Tatler.
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   5. To become indifferent; to cease to be subject; as, to die
      to pleasure or to sin.
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   6. To recede and grow fainter; to become imperceptible; to
      vanish; -- often with out or away.
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            Blemishes may die away and disappear amidst the
            brightness.                           --Spectator.
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   7. (Arch.) To disappear gradually in another surface, as
      where moldings are lost in a sloped or curved face.
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   8. To become vapid, flat, or spiritless, as liquor.
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   To die in the last ditch, to fight till death; to die
      rather than surrender.
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            "There is one certain way," replied the Prince
            [William of Orange] " by which I can be sure never
            to see my country's ruin, -- I will die in the last
            ditch."                               --Hume (Hist.
                                                  of Eng. ).

   To die out, to cease gradually; as, the prejudice has died
      out.

   Syn: To expire; decease; perish; depart; vanish.
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The Collaborative International Dictionary of English v.0.48:

Dying \Dy"ing\, a.
   1. In the act of dying; destined to death; mortal;
      perishable; as, dying bodies.
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   2. Of or pertaining to dying or death; as, dying bed; dying
      day; dying words; also, simulating a dying state.
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The Collaborative International Dictionary of English v.0.48:

Dying \Dy"ing\, n.
   The act of expiring; passage from life to death; loss of
   life.
   [1913 Webster]

WordNet (r) 3.0 (2006):

dying
    adj 1: in or associated with the process of passing from life or
           ceasing to be; "a dying man"; "his dying wish"; "a dying
           fire"; "a dying civilization" [ant: nascent]
    2: eagerly desirous; "anxious to see the new show at the
       museum"; "dying to hear who won" [syn: anxious(p),
       dying(p)]
    n 1: the time when something ends; "it was the death of all his
         plans"; "a dying of old hopes" [syn: death, dying,
         demise] [ant: birth]

Moby Thesaurus II by Grady Ward, 1.0:

208 Moby Thesaurus words for "dying":
   abatement, abridgment, alleviation, annihilation, attenuation, bad,
   bane, biological death, brittle, burning out, burnout, capricious,
   cessation of life, changeable, choking, clinical death, comedown,
   contraction, controlling, corruptible, crossing the bar, curtains,
   dampening, damping, death, death knell, debasement, debt of nature,
   decadence, decadency, decease, deciduous, declension, declination,
   decline, declining, decrease, decrement, decrescence, deduction,
   deflation, deformation, degeneracy, degenerateness, degeneration,
   degradation, demise, demotion, departure, depravation,
   depravedness, depreciation, depression, derogation, descent,
   despaired of, deterioration, devolution, diminishing, diminishment,
   diminution, dissolution, done for, doom, dousing, downtrend,
   downturn, downward mobility, downward trend, drop, dwindling,
   dying off, ebb, ebb of life, ebbing, effeteness, end, end of life,
   ending, ephemeral, eternal rest, evanescent, exit, expiration,
   expiring, extenuation, extinction, extinguishment, facing death,
   fade-out, fading, failing, failure, failure of nerve, fall,
   falling-off, fickle, final summons, finger of death, fire fighting,
   flame-out, fleeting, flitting, fly-by-night, flying, fragile,
   frail, fugacious, fugitive, given up, going, going off, going out,
   grave, hand of death, hopeless, impermanent, impetuous, impulsive,
   in articulo mortis, in extremis, incapable of life, inconstant,
   insubstantial, involution, jaws of death, knell, languishment,
   lapse, last debt, last muster, last rest, last roundup, last sleep,
   leaving life, lessening, letup, loss of life, loss of tone, low,
   lowering, making an end, miniaturization, mitigation, momentary,
   moribund, mortal, mutable, near death, nondurable, nonpermanent,
   nonviable, parting, passing, passing away, passing over,
   perishable, perishing, putting out, quenching, quietus, receding,
   reduction, regression, relaxation, release, rest, retiring,
   retreating, retrocession, retrogradation, retrogression, reward,
   sagging, scaling down, sentence of death, shades of death,
   shadow of death, short-lived, shrinking, simplicity, sinking,
   sleep, slippage, slipping, slipping away, slump, smotheration,
   smothering, snuffing, somatic death, stifling, subtraction,
   summons of death, temporal, temporary, terminal, terminal case,
   transient, transitive, transitory, undurable, unenduring, unstable,
   volatile, wane, waning, weakening