The Collaborative International Dictionary of English v.0.48:

Perpetual \Per*pet"u*al\, a. [OE. perpetuel, F. perp['e]tuel,
   fr. L. perpetualis, fr. perpetuus continuing throughout,
   continuous, fr. perpes, -etis, lasting throughout.]
   Neverceasing; continuing forever or for an unlimited time;
   unfailing; everlasting; continuous.
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         Unto the kingdom of perpetual night.     --Shak.
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         Perpetual feast of nectared sweets.      --Milton.
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   Circle of perpetual apparition, or Circle of perpetual
   occultation. See under Circle.

   Perpetual calendar, a calendar so devised that it may be
      adjusted for any month or year.

   Perpetual curacy (Ch. of Eng.), a curacy in which all the
      tithes are appropriated, and no vicarage is endowed.
      --Blackstone.

   Perpetual motion. See under Motion.

   Perpetual screw. See Endless screw, under Screw.
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   Syn: Continual; unceasing; endless; everlasting; incessant;
        constant; eternal. See Constant.
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The Collaborative International Dictionary of English v.0.48:

Tax \Tax\, n. [F. taxe, fr. taxer to tax, L. taxare to touch,
   sharply, to feel, handle, to censure, value, estimate, fr.
   tangere, tactum, to touch. See Tangent, and cf. Task,
   Taste.]
   1. A charge, especially a pecuniary burden which is imposed
      by authority. Specifically:
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      (a) A charge or burden laid upon persons or property for
          the support of a government.
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                A farmer of taxes is, of all creditors,
                proverbially the most rapacious.  --Macaulay.
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      (b) Especially, the sum laid upon specific things, as upon
          polls, lands, houses, income, etc.; as, a land tax; a
          window tax; a tax on carriages, and the like.

   Note: Taxes are annual or perpetual, direct or
         indirect, etc.
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      (c) A sum imposed or levied upon the members of a society
          to defray its expenses.
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   2. A task exacted from one who is under control; a
      contribution or service, the rendering of which is imposed
      upon a subject.
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   3. A disagreeable or burdensome duty or charge; as, a heavy
      tax on time or health.
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   4. Charge; censure. [Obs.] --Clarendon.
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   5. A lesson to be learned; a task. [Obs.] --Johnson.
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   Tax cart, a spring cart subject to a low tax. [Eng.]
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   Syn: Impost; tribute; contribution; duty; toll; rate;
        assessment; exaction; custom; demand.
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WordNet (r) 3.0 (2006):

perpetual
    adj 1: continuing forever or indefinitely; "the ageless themes
           of love and revenge"; "eternal truths"; "life
           everlasting"; "hell's perpetual fires"; "the unending
           bliss of heaven" [syn: ageless, aeonian, eonian,
           eternal, everlasting, perpetual, unending,
           unceasing]
    2: uninterrupted in time and indefinitely long continuing; "the
       ceaseless thunder of surf"; "in constant pain"; "night and
       day we live with the incessant noise of the city"; "the
       never-ending search for happiness"; "the perpetual struggle
       to maintain standards in a democracy"; "man's unceasing
       warfare with drought and isolation"; "unremitting demands of
       hunger" [syn: ceaseless, constant, incessant, never-
       ending, perpetual, unceasing, unremitting]