The Collaborative International Dictionary of English v.0.48:

Modesty \Mod"es*ty\, n. [L. modestia: cf. F. modestie. See
   Modest.]
   1. The quality or state of being modest; that lowly temper
      which accompanies a moderate estimate of one's own worth
      and importance; absence of self-assertion, arrogance, and
      presumption; humility respecting one's own merit.
      [1913 Webster]

   2. Natural delicacy or shame regarding personal charms and
      the sexual relation; purity of thought and manners; due
      regard for propriety in speech or action.
      [1913 Webster]

            Her blush is guiltiness, not modesty. --Shak.
      [1913 Webster]

   Modesty piece, a narrow piece of lace worn by women over
      the bosom. [Obs.] --Addison.
      [1913 Webster]

   Syn: Bashfulness; humility; diffidence; shyness. See
        Bashfulness, and Humility.
        [1913 Webster]

WordNet (r) 3.0 (2006):

modesty
    n 1: freedom from vanity or conceit [syn: modesty,
         modestness] [ant: immodesty]
    2: formality and propriety of manner [syn: modesty, reserve]

Moby Thesaurus II by Grady Ward, 1.0:

128 Moby Thesaurus words for "modesty":
   aloofness, altruism, backwardness, bashfulness, blankness, boggle,
   boggling, chilliness, coldness, commitment, compunction,
   consecration, constraint, coolness, decency, decorousness, decorum,
   dedication, delicacy, demur, demurral, detachment, devotion,
   diffidence, discreetness, discretion, disinterest,
   disinterestedness, distance, dullness, elegance,
   expressionlessness, fairishness, falter, faltering, frigidity,
   frostiness, guardedness, hesitance, hesitancy, hesitation,
   homeliness, humbleness, humility, iciness, impassiveness,
   impassivity, impersonality, inaccessibility, indifference,
   ingloriousness, innocuousness, introversion, lackluster, lowlihood,
   lowliness, meanness, mediocreness, mediocrity, meekness,
   middlingness, moderateness, modestness, objection, passableness,
   pause, plainness, poorness, propriety, protest, pudency, pudicity,
   qualm, qualm of conscience, qualmishness, recoil, remoteness,
   repression, reserve, reservedness, respectability, restraint,
   reticence, reticency, retirement, sacrifice, scruple, scrupulosity,
   scrupulousness, seemliness, self-abasement, self-abnegation,
   self-denial, self-devotion, self-effacement, self-forgetfulness,
   self-immolation, self-neglect, self-neglectfulness,
   self-renouncement, self-sacrifice, self-subjection, selflessness,
   shame, shrinking, shyness, simpleness, smallness, standoffishness,
   stickling, subduedness, submissiveness, suppression, teachableness,
   tediousness, tolerableness, unacquisitiveness, unaffability,
   unapproachability, uncongeniality, undemonstrativeness,
   unexpansiveness, unimportance, unpossessiveness, unpretentiousness,
   unselfishness, withdrawal, withdrawnness