The Collaborative International Dictionary of English v.0.48:

Vary \Va"ry\, v. t. [imp. & p. p. Varied; p. pr. & vb. n.
   Varying.] [OE. varien, F. varier, L. variare, fr. varius
   various. See Various, and cf. Variate.]
   [1913 Webster]
   1. To change the aspect of; to alter in form, appearance,
      substance, position, or the like; to make different by a
      partial change; to modify; as, to vary the properties,
      proportions, or nature of a thing; to vary a posture or an
      attitude; to vary one's dress or opinions.
      [1913 Webster]

            Shall we vary our device at will,
            Even as new occasion appears?         --Spenser.
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   2. To change to something else; to transmute; to exchange; to
      alternate.
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            Gods, that never change their state,
            Vary oft their love and hate.         --Waller.
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            We are to vary the customs according to the time and
            country where the scene of action lies. --Dryden.
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   3. To make of different kinds; to make different from one
      another; to diversify; to variegate.
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            God hath varied their inclinations.   --Sir T.
                                                  Browne.
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            God hath here
            Varied his bounty so with new delights. --Milton.
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   4. (Mus.) To embellish; to change fancifully; to present
      under new aspects, as of form, key, measure, etc. See
      Variation, 4.
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The Collaborative International Dictionary of English v.0.48:

Vary \Va"ry\, n.
   Alteration; change. [Obs.] --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Vary \Va"ry\, v. i.
   1. To alter, or be altered, in any manner; to suffer a
      partial change; to become different; to be modified; as,
      colors vary in different lights.
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            That each from other differs, first confess;
            Next, that he varies from himself no less. --Pope.
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   2. To differ, or be different; to be unlike or diverse; as,
      the laws of France vary from those of England.
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   3. To alter or change in succession; to alternate; as, one
      mathematical quantity varies inversely as another.
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            While fear and anger, with alternate grace,
            Pant in her breast, and vary in her face. --Addison.
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   4. To deviate; to depart; to swerve; -- followed by from; as,
      to vary from the law, or from reason. -- Locke.
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   5. To disagree; to be at variance or in dissension; as, men
      vary in opinion.
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            The rich jewel which we vary for.     --Webster
                                                  (1623).
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WordNet (r) 3.0 (2006):

vary
    v 1: become different in some particular way, without
         permanently losing one's or its former characteristics or
         essence; "her mood changes in accordance with the weather";
         "The supermarket's selection of vegetables varies according
         to the season" [syn: change, alter, vary]
    2: be at variance with; be out of line with [syn: deviate,
       vary, diverge, depart] [ant: conform]
    3: be subject to change in accordance with a variable; "Prices
       vary"; "His moods vary depending on the weather"
    4: make something more diverse and varied; "Vary the menu" [syn:
       vary, variegate, motley]

Moby Thesaurus II by Grady Ward, 1.0:

194 Moby Thesaurus words for "vary":
   accommodate, adapt, adjust, agree to disagree, alter, alternate,
   ameliorate, analyze, anatomize, atomize, back and fill,
   be at cross-purposes, be changed, be converted into, be distinct,
   be distinguished, be renewed, bear off, bend, better, bottom out,
   branch off, break, break off, break up, camouflage, change,
   change the bearing, checker, chop, chop and change, chop logic,
   clash, clash with, collide, come about, come around, come round,
   conflict, conflict with, contradict, contrast with, convert,
   counter, curve, deform, degenerate, denature, depart, depart from,
   desynonymize, deteriorate, detour, deviate, deviate from, differ,
   difference, differentiate, digress, disaccord, disaccord with,
   disagree, disagree with, discord, discriminate, disequalize,
   disguise, disjoin, dissent, dissimilate, distinguish, disunify,
   dither, divagate, divaricate, divaricate from, diverge,
   diverge from, diversify, divide, ebb and flow, equivocate, extend,
   fit, flop, flounder, fluctuate, go, go through phases, haul around,
   heel, improve, individualize, individuate, intermit, jangle, jar,
   jar with, jibe, jostle, lack regularity, make a distinction, mark,
   mark off, mark out, meliorate, mismatch, mismate, mitigate, modify,
   modulate, mutate, negate, not accord with, not square with, object,
   oscillate, overthrow, part, particularize, pendulate, personalize,
   qualify, re-create, realign, rebuild, reconstruct, redesign,
   refashion, refine a distinction, refit, reform, relieve, remake,
   remodel, renew, reorganize, reshape, restructure, revamp, revive,
   ring changes, ring the changes, run, seesaw, segregate, separate,
   set apart, set off, sever, severalize, sheer, shift,
   shift the scene, shilly-shally, shuffle, shuffle the cards,
   specialize, split hairs, stagger, stand apart, stand over against,
   subvert, sway, swerve, swing, switch, tack, take a turn, teeter,
   teeter-totter, tergiversate, totter, transform, trend, turn,
   turn aside, turn into, turn the corner, turn the scale,
   turn the tables, turn the tide, turn upside down, undergo a change,
   vacillate, variate, variegate, veer, warp, waver, wax and wane,
   wobble, work a change, worsen