The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

   2. The state or result of having deviated; a transgression;
      an act of sin; an error; an offense.
      [1913 Webster]

   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.
      [1913 Webster]

   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.
      [1913 Webster]

WordNet (r) 3.0 (2006):

deviation
    n 1: a variation that deviates from the standard or norm; "the
         deviation from the mean" [syn: deviation, divergence,
         departure, difference]
    2: the difference between an observed value and the expected
       value of a variable or function
    3: the error of a compass due to local magnetic disturbances
    4: deviate behavior [syn: deviation, deviance]
    5: a turning aside (of your course or attention or concern); "a
       diversion from the main highway"; "a digression into
       irrelevant details"; "a deflection from his goal" [syn:
       diversion, deviation, digression, deflection,
       deflexion, divagation]

Moby Thesaurus II by Grady Ward, 1.0:

309 Moby Thesaurus words for "deviation":
   aberrance, aberrancy, aberration, abnormality, abnormity,
   about-face, accommodation, adaptation, adjustment, allowance,
   alteration, ambages, amelioration, amorphism, anamorphism,
   anamorphosis, anomalism, anomalousness, anomaly, apostasy,
   approximation, asymmetry, bend, betterment, blunder, breach, break,
   buckle, bypass, bypath, byway, capriciousness, centrifugence,
   change, change of heart, changeability, changeableness, choppiness,
   circling, circuit, circuition, circuitousness, circuitry,
   circularity, circulation, circumambience, circumambiency,
   circumambulation, circumbendibus, circumflexion, circumlocution,
   circummigration, circumnavigation, conceit, constructive change,
   continuity, contortion, contrariety, contrast, conversion,
   crackpotism, crank, crankiness, crankism, crookedness,
   crosswiseness, crotchet, crotchetiness, dappleness,
   decentralization, declination, defection, deflection, deflexure,
   degeneration, degenerative change, departure, deployment,
   derangement, deterioration, detorsion, detour, deviance, deviancy,
   deviousness, diagonality, difference, differentiation,
   differentness, digression, disaccord, disaccordance, disagreement,
   disconformity, discongruity, discontinuity, discordance,
   discrepancy, discreteness, discursion, disorder, disparity,
   disproportion, dissent, dissimilarity, dissonance, distinction,
   distinctness, distortion, divagation, divarication, divergence,
   divergency, diversification, diversion, diversity, division,
   dottiness, double, eccentricity, episode, erraticism, erraticness,
   error, excursion, excursus, failing, fanning, fanning out, far cry,
   fault, fitting, flip-flop, freakiness, freakishness, gnarl,
   gradual change, gyre, gyring, heterogeneity, heteromorphism,
   idiocrasy, idiosyncrasy, imbalance, imprecision, improvement,
   inaccordance, inaccuracy, inaccurateness, incompatibility,
   incongruity, inconsistency, inconsonance, inconstancy,
   incorrectness, indirection, indirectness, inequality, inexactitude,
   inexactness, inferiority, inharmoniousness, inharmony, instability,
   irreconcilability, irregularity, jerkiness, kink, knot, lapse,
   laxity, looseness, lopsidedness, maggot, mannerism, meandering,
   melioration, mercuriality, mitigation, mixture, modification,
   modulation, monstrosity, motleyness, mutability, negligence,
   noncompliance, nonconcurrence, nonconformance, nonconformism,
   nonconformity, nonobservance, nonstandardization, nonuniformity,
   obliqueness, obliquity, oddity, odds, opposition, orbit, orbiting,
   originality, otherness, overthrow, peculiarity, pluralism,
   predictable error, probable error, protest, qualification,
   queerness, quip, quirk, quirkiness, radical change, raggedness,
   re-creation, realignment, recalcitrance, recusance, recusancy,
   redesign, reform, reformation, refractoriness, remaking, renewal,
   reshaping, restructuring, reversal, revival, revivification,
   revolution, roundabout, roundabout way, roundaboutness, rounding,
   screw, separateness, separation, shift, side path, side road,
   sidetrack, singularity, skewness, spiral, spiraling, splaying,
   spread, spreading, spreading out, squint, standard deviation,
   strangeness, subnormality, sudden change, superiority, switch,
   tack, teratism, tolerance, torsion, tortuosity, total change,
   transgression, transition, transverseness, trick, turn, turnabout,
   turning, twist, unconformism, unconformity, unconventionality,
   uncorrectness, unevenness, unfactualness, unlikeness, unnaturalism,
   unnaturalness, unorthodoxy, unpreciseness, unrigorousness,
   unsteadiness, unsymmetry, upheaval, vagary, variability, variance,
   variation, variegation, variety, variousness, versatility,
   violation, violent change, warp, wavering, wheeling, whim,
   whimsicality, whimsy, worsening, wrench, wrest, wring, yaw



Bouvier's Law Dictionary, Revised 6th Ed (1856):

DEVIATION, insurance, contracts. A voluntary departure, without necessity,
or any reasonable cause, from the regular and usual course of the voyage
insured.
     2. From the moment this happens, the voyage is changed, the contract
determined, and the insurer discharged from all subsequent responsibility.
By the contract, the insurer only runs the risk of the contract agreed upon,
and no other; and it is, therefore, a condition implied in the policy, that
the ship shall proceed to her port of destination by the. shortest and
safest course, and on no account to deviate from that course, but in cases
of necessity. 1 Mood. & Rob. 60; 17 Ves. 364; 3 Bing. 637; 12 East, 578.
     3. The effect of a deviation is not to vitiate or avoid the policy, but
only to determine the liability of the underwriters from the time of the
deviation. If, therefore, the ship or goods, after the voyage has commenced,
receive damage, then the ship deviates, and afterwards a loss happen, there,
though the insurer is discharged from the time of the deviation, and is not
answerable for the subsequent loss, yet he is bound to make good the damage
sustained previous to the deviation. 2 Lord Raym. 842 2 Salk. 444.
     4. But though he is thus discharged from subsequent responsibility, he
is entitled to retain the whole premium. Dougl. 271; 1 Marsh. Ins. 183;
Park. Ins. 294. See 2 Phil. Ev. 60, n. (b) where the American cases are
cited.
     5. What amounts to a deviation is not easily defined, but a departure
from the usual course of the voyage, or remaining at places where the ship
is authorized to touch, longer than necessary, or doing there what the
insured is not authorized to do; as, if the ship have merely liberty to
touch at a point, and the insured stay there to trade, or break bulk, it is
a deviation. 4 Dall. 274 1 Peters' C. C. R. 104; Marsh. Ins. B. 1, c. 6, s.
2. By the course of the voyage is not meant the shortest course the ship can
take from her port of departure to her port of destination, but the regular
and customary track, if such there be, which long us usage has proved to be
the safest and most convenient. 1 Marsh. Ins. 185. See 3 Johns. Cas. 352; 7
T. R. 162.
     6. A deviation that will discharge the insurer, must be a voluntary
departure from the usual course of the voyage insured, and not warranted by
any necessity. If a deviation can be justified by necessity, it will not
affect the contract; and necessity will justify a deviation, though it
proceed from a cause not insured against. The cases of necessity which are
most frequently adduced to justify a departure from the direct or usual
course of the voyage, are, 1st. Stress of weather. 2d. The want of necessary
repairs. 3d. Joining convoy. 4th. Succouring ships in distress. 5th.
Avoiding capture or detention. 6th. Sickness of the master or mariner. 7th.
Mutiny of the crew. See Park, Ins. c. 17; 1 Bouv. Inst. n. 1187, et seq.; 2
John. Cas. 296; 11 Johns. R. 241; Pet. C. C. R. 98; 2 Johns. Rep. 89; 14
Johns. R. 315; 2 Johns. R. 138; 9 Johns. R. 192; 8 Johns. Rep. 491; 13 Mass.
68 13 Mass. 539; Id. 118; 14 Mass. 12 1 Johns. Cas. 313; 11 Johns. R. 241; 3
Johns. R. 352; 10 Johns. R. 83; 1 Johns. R. 301; 9 Mass. 436, 447; 3 Binn.
457 7 Mass. 349; 5 Mass. 1; 8 Mass. 308 6 Mass. 102 121 6 Mass. 122 7
Cranch, 26; Id. 487; 3 Wheat. 159 7 Mass. 365; 10 Mass. 21 Id. 347 7 Johns.
Rep. 864; 3 Johns. R. 352; 4 Dall. R. 274 5 Binn. 403; 2 Serg. & Raw. 309; 2
Cranch, 240.



Bouvier's Law Dictionary, Revised 6th Ed (1856):

DEVIATION, contracts. When a plan has been adopted for a building, and in
the progress of the work a change has been made from the original plan, the
change is called a deviation.
     2. When the contract is to build a house according to the original
plan, and a deviation takes place, the contract shall be traced as far as
possible, and the additions, if any have been made, shall be paid for
according to the usual rate of charging. 3 Barn. & Ald. 47; and see 1 Ves.
jr. 60; 10 Ves. jr. 306; 14 Ves. 413; 13 Ves. 73; Id. 81 6 Johns. Ch. R. 38;
3 Cranch, 270; 5 Cranch, 262; 3 Ves. 693; 7 Ves. 274; Chit. Contr. 168; 9
Pick. 298.
     3. The Civil Code of Louisiana, art. 2734, provides, that when an
architect or other workman has undertaken the building of a house by the
job, according to a plot agreed on between him and the owner of the ground,
he cannot claim an increase of the price agreed on, on the plea of the
original plot having been changed and extended, unless he can prove that
such changes have been made in compliance with the wishes of the proprietor.