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:

Motion \Mo"tion\, n. [F., fr. L. motio, fr. movere, motum, to
   move. See Move.]
   1. The act, process, or state of changing place or position;
      movement; the passing of a body from one place or position
      to another, whether voluntary or involuntary; -- opposed
      to rest.
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            Speaking or mute, all comeliness and grace
            attends thee, and each word, each motion, forms.
                                                  --Milton.
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   2. Power of, or capacity for, motion.
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            Devoid of sense and motion.           --Milton.
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   3. Direction of movement; course; tendency; as, the motion of
      the planets is from west to east.
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            In our proper motion we ascend.       --Milton.
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   4. Change in the relative position of the parts of anything;
      action of a machine with respect to the relative movement
      of its parts.
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            This is the great wheel to which the clock owes its
            motion.                               --Dr. H. More.
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   5. Movement of the mind, desires, or passions; mental act, or
      impulse to any action; internal activity.
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            Let a good man obey every good motion rising in his
            heart, knowing that every such motion proceeds from
            God.                                  --South.
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   6. A proposal or suggestion looking to action or progress;
      esp., a formal proposal made in a deliberative assembly;
      as, a motion to adjourn.
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            Yes, I agree, and thank you for your motion. --Shak.
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   7. (Law) An application made to a court or judge orally in
      open court. Its object is to obtain an order or rule
      directing some act to be done in favor of the applicant.
      --Mozley & W.
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   8. (Mus.) Change of pitch in successive sounds, whether in
      the same part or in groups of parts.
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            The independent motions of different parts sounding
            together constitute counterpoint.     --Grove.
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   Note: Conjunct motion is that by single degrees of the scale.
         Contrary motion is that when parts move in opposite
         directions. Disjunct motion is motion by skips. Oblique
         motion is that when one part is stationary while
         another moves. Similar or direct motion is that when
         parts move in the same direction.
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   9. A puppet show or puppet. [Obs.]
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            What motion's this? the model of Nineveh? --Beau. &
                                                  Fl.
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   Note: Motion, in mechanics, may be simple or compound.

   Simple motions are: (a) straight translation, which, if
      of indefinite duration, must be reciprocating. (b)
      Simple rotation, which may be either continuous or
      reciprocating, and when reciprocating is called
      oscillating. (c) Helical, which, if of indefinite
      duration, must be reciprocating.

   Compound motion consists of combinations of any of the
      simple motions.
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   Center of motion, Harmonic motion, etc. See under
      Center, Harmonic, etc.

   Motion block (Steam Engine), a crosshead.

   Perpetual motion (Mech.), an incessant motion conceived to
      be attainable by a machine supplying its own motive forces
      independently of any action from without. According to the
      law of conservation of energy, such perpetual motion is
      impossible, and no device has yet been built that is
      capable of perpetual motion.
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   Syn: See Movement.
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WordNet (r) 3.0 (2006):

perpetual motion
    n 1: motion that continues indefinitely without any external
         source of energy; impossible in practice because of
         friction