The Collaborative International Dictionary of English v.0.48:

Evenness \E"ven*ness\, n.
   The state of being ven, level, or disturbed; smoothness;
   horizontal position; uniformity; impartiality; calmness;
   equanimity; appropriate place or level; as, evenness of
   surface, of a fluid at rest, of motion, of dealings, of
   temper, of condition.
   [1913 Webster]

         It had need be something extraordinary, that must
         warrant an ordinary person to rise higher than his own
         evenness.                                --Jer. Taylor.
   [1913 Webster]

WordNet (r) 3.0 (2006):

evenness
    n 1: the parity of even numbers (divisible by two)
    2: a quality of uniformity and lack of variation [syn:
       evenness, invariability] [ant: unevenness,
       variability]
    3: the quality of being balanced [ant: unevenness]

Moby Thesaurus II by Grady Ward, 1.0:

125 Moby Thesaurus words for "evenness":
   abnegation, abstinence, accordance, balance, bilateral symmetry,
   calm, calmness, clockwork regularity, coequality, coextension,
   conformity, congruity, conservatism, consistency, consonance,
   constancy, constraint, continence, continuity, control, cool,
   correspondence, dispassion, downiness, dynamic symmetry,
   equability, equality, equanimity, equation, equilibrium, equipoise,
   equipollence, equiponderance, equity, equivalence, equivalency,
   eurythmics, eurythmy, finish, flatness, flushness,
   frictionlessness, gentleness, glabriety, glabrousness, glossiness,
   golden mean, greasiness, happy medium, harmony, homogeneity,
   horizontalism, horizontality, horizontalness, identity,
   impartiality, judiciousness, juste-milieu, justice, keeping,
   lenity, levelness, likeness, lubricity, meden agan, methodicalness,
   middle way, mildness, moderateness, moderation, moderationism,
   monolithism, multilateral symmetry, neutrality, nonviolence,
   nothing in excess, oiliness, pacifism, par, parallelism, parity,
   persistence, planeness, poise, polarity, proportion,
   proportionality, prudence, punctuality, regularity, repetition,
   repose, restraint, satininess, self-abnegation, self-control,
   self-denial, self-restraint, serenity, shapeliness, silkiness,
   sleekness, slickness, slipperiness, smoothness, sobriety,
   stability, steadfastness, steadiness, suavity, symmetricalness,
   symmetry, systematicalness, temperance, temperateness,
   tranquillity, trilateral symmetry, unexcessiveness, unextravagance,
   unextremeness, uniformity, unity, unruffledness, velvetiness,
   via media