deviation \de`vi*a"tion\, n. [LL. deviatio: cf. F.
   d['e]viation.]
   1. The act of deviating; a wandering from the way; variation
      from the common way, from an established rule, etc.;
      departure, as from the right course or the path of duty.
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   2. The state or result of having deviated; a transgression;
      an act of sin; an error; an offense.
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   3. (Com.) The voluntary and unnecessary departure of a ship
      from, or delay in, the regular and usual course of the
      specific voyage insured, thus releasing the underwriters
      from their responsibility.
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   4. (Statistics, Physics) the difference between an expected
      value of an observation or measurement and the actual
      value.
      [PJC]

   Deviation of a falling body (Physics), that deviation from
      a strictly vertical line of descent which occurs in a body
      falling freely, in consequence of the rotation of the
      earth.

   Deviation of the compass, the angle which the needle of a
      ship's compass makes with the magnetic meridian by reason
      of the magnetism of the iron parts of the ship.

   Deviation of the line of the vertical, the difference
      between the actual direction of a plumb line and the
      direction it would have if the earth were a perfect
      ellipsoid and homogeneous, -- caused by the attraction of
      a mountain, or irregularities in the earth's density.
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