The Collaborative International Dictionary of English v.0.48:

Variant \Va"ri*ant\, n. [Cf. F. variante.]
   Something which differs in form from another thing, though
   really the same; as, a variant from a type in natural
   history; a variant of a story or a word.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Variant \Va"ri*ant\, a. [L. varians, p. pr. of variare to
   change: cf. F. variant. See Vary.]
   1. Varying in form, character, or the like; variable;
      different; diverse.
      [1913 Webster]

   2. Changeable; changing; fickle. [Obs.]
      [1913 Webster]

            He is so variant, he abit [abides] nowhere.
                                                  --Chaucer.
      [1913 Webster]

WordNet (r) 3.0 (2006):

variant
    adj 1: differing from a norm or standard; "a variant spelling"
    2: exhibiting variation and change; "letters variant in size"
    n 1: an event that departs from expectations [syn:
         discrepancy, variance, variant]
    2: (biology) a group of organisms within a species that differ
       in trivial ways from similar groups; "a new strain of
       microorganisms" [syn: form, variant, strain, var.]
    3: a variable quantity that is random [syn: random variable,
       variate, variant, stochastic variable, chance
       variable]
    4: something a little different from others of the same type;
       "an experimental version of the night fighter"; "a variant of
       the same word"; "an emery wheel is the modern variation of a
       grindstone"; "the boy is a younger edition of his father"
       [syn: version, variant, variation, edition]

Moby Thesaurus II by Grady Ward, 1.0:

87 Moby Thesaurus words for "variant":
   altering, alternative, antagonistic, antipathetic, assorted,
   at cross-purposes, at loggerheads, at odds, at variance, at war,
   changing, clashing, contradictory, contrary, contrasted,
   contrasting, cranky, cross, departing, deviant, deviating,
   deviative, different, differentiated, differing, disaccordant,
   disagreeable, disagreeing, discordant, discrepant, discrete,
   discriminated, disharmonious, disjoined, disparate,
   disproportionate, dissident, dissimilar, dissonant, distinct,
   distinguished, divergent, diverging, divers, diverse, diversified,
   grating, heterogeneous, hostile, immiscible, in disagreement,
   inaccordant, incompatible, incongruous, inconsistent, inconsonant,
   inharmonious, irreconcilable, jangling, jarring, many,
   modification, motley, multifarious, negative, out of accord,
   out of whack, poles apart, poles asunder, repugnant, separate,
   separated, several, unconformable, uncongenial, unequal,
   unharmonious, unlike, unstable, variable, variation, varied,
   variegated, various, varying, widely apart, worlds apart