The Collaborative International Dictionary of English v.0.48:

Harmonic \Har*mon"ic\ (h[aum]r*m[o^]n"[i^]k), Harmonical
\Har*mon"ic*al\ (-[i^]*kal), a. [L. harmonicus, Gr. "armoniko`s;
   cf. F. harmonique. See Harmony.]
   1. Concordant; musical; consonant; as, harmonic sounds.
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            Harmonic twang! of leather, horn, and brass. --Pope.
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   2. (Mus.) Relating to harmony, -- as melodic relates to
      melody; harmonious; esp., relating to the accessory sounds
      or overtones which accompany the predominant and apparent
      single tone of any string or sonorous body.
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   3. (Math.) Having relations or properties bearing some
      resemblance to those of musical consonances; -- said of
      certain numbers, ratios, proportions, points, lines,
      motions, and the like.
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   Harmonic interval (Mus.), the distance between two notes of
      a chord, or two consonant notes.

   Harmonical mean (Arith. & Alg.), certain relations of
      numbers and quantities, which bear an analogy to musical
      consonances.

   Harmonic motion, the motion of the point A, of the foot of
      the perpendicular PA, when P moves uniformly in the
      circumference of a circle, and PA is drawn perpendicularly
      upon a fixed diameter of the circle. This is simple
      harmonic motion. The combinations, in any way, of two or
      more simple harmonic motions, make other kinds of harmonic
      motion. The motion of the pendulum bob of a clock is
      approximately simple harmonic motion.

   Harmonic proportion. See under Proportion.

   Harmonic series or Harmonic progression. See under
      Progression.

   Spherical harmonic analysis, a mathematical method,
      sometimes referred to as that of Laplace's Coefficients,
      which has for its object the expression of an arbitrary,
      periodic function of two independent variables, in the
      proper form for a large class of physical problems,
      involving arbitrary data, over a spherical surface, and
      the deduction of solutions for every point of space. The
      functions employed in this method are called spherical
      harmonic functions. --Thomson & Tait.

   Harmonic suture (Anat.), an articulation by simple
      apposition of comparatively smooth surfaces or edges, as
      between the two superior maxillary bones in man; -- called
      also harmonia, and harmony.

   Harmonic triad (Mus.), the chord of a note with its third
      and fifth; the common chord.
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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):

harmonic motion
    n 1: a periodic motion in which the displacement is either
         symmetrical about a point or is the sum of such motions