The Collaborative International Dictionary of English v.0.48:

Variation \Va`ri*a"tion\, n. [OE. variatioun, F. variation, L.
   variatio. See Vary.]
   1. The act of varying; a partial change in the form,
      position, state, or qualities of a thing; modification;
      alteration; mutation; diversity; deviation; as, a
      variation of color in different lights; a variation in
      size; variation of language.
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            The essences of things are conceived not capable of
            any such variation.                   --Locke.
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   2. Extent to which a thing varies; amount of departure from a
      position or state; amount or rate of change.
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   3. (Gram.) Change of termination of words, as in declension,
      conjugation, derivation, etc.
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   4. (Mus.) Repetition of a theme or melody with fanciful
      embellishments or modifications, in time, tune, or
      harmony, or sometimes change of key; the presentation of a
      musical thought in new and varied aspects, yet so that the
      essential features of the original shall still preserve
      their identity.
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   5. (Alg.) One of the different arrangements which can be made
      of any number of quantities taking a certain number of
      them together.
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   Annual variation (Astron.), the yearly change in the right
      ascension or declination of a star, produced by the
      combined effects of the precession of the equinoxes and
      the proper motion of the star.

   Calculus of variations. See under Calculus.

   Variation compass. See under Compass.

   Variation of the moon (Astron.), an inequality of the
      moon's motion, depending on the angular distance of the
      moon from the sun. It is greater at the octants, and zero
      at the quadratures.

   Variation of the needle (Geog. & Naut.), the angle included
      between the true and magnetic meridians of a place; the
      deviation of the direction of a magnetic needle from the
      true north and south line; -- called also declination of
      the needle.
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   Syn: Change; vicissitude; variety; deviation.
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The Collaborative International Dictionary of English v.0.48:

Declination \Dec`li*na"tion\, n. [L. declinatio a bending aside,
   an avoiding: cf. F. d['e]clination a decadence. See
   Declension.]
   1. The act or state of bending downward; inclination; as,
      declination of the head.
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   2. The act or state of falling off or declining from
      excellence or perfection; deterioration; decay; decline.
      "The declination of monarchy." --Bacon.
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            Summer . . . is not looked on as a time
            Of declination or decay.              --Waller.
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   3. The act of deviating or turning aside; oblique motion;
      obliquity; withdrawal.
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            The declination of atoms in their descent.
                                                  --Bentley.
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            Every declination and violation of the rules.
                                                  --South.
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   4. The act or state of declining or refusing; withdrawal;
      refusal; averseness.
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            The queen's declination from marriage. --Stow.
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   5. (Astron.) The angular distance of any object from the
      celestial equator, either northward or southward.
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   6. (Dialing) The arc of the horizon, contained between the
      vertical plane and the prime vertical circle, if reckoned
      from the east or west, or between the meridian and the
      plane, reckoned from the north or south.
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   7. (Gram.) The act of inflecting a word; declension. See
      Decline, v. t., 4.
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   Angle of declination, the angle made by a descending line,
      or plane, with a horizontal plane.

   Circle of declination, a circle parallel to the celestial
      equator.

   Declination compass (Physics), a compass arranged for
      finding the declination of the magnetic needle.

   Declination of the compass or Declination of the needle,
      the horizontal angle which the magnetic needle makes with
      the true north-and-south line.
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