The Collaborative International Dictionary of English v.0.48:

Nobility \No*bil"i*ty\, n. [L. nobilitas: cf. OF. nobilit['e].
   See Noble.]
   1. The quality or state of being noble; superiority of mind
      or of character; commanding excellence; eminence.
      [1913 Webster]

            Though she hated Amphialus, yet the nobility of her
            courage prevailed over it.            --Sir P.
                                                  Sidney.
      [1913 Webster]

            They thought it great their sovereign to control,
            And named their pride nobility of soul. --Dryden.
      [1913 Webster]

   2. The state of being of high rank or noble birth; patrician
      dignity; antiquity of family; distinction by rank,
      station, or title, whether inherited or conferred.
      [1913 Webster]

            I fell on the same argument of preferring virtue to
            nobility of blood and titles, in the story of
            Sigismunda.                           --Dryden.
      [1913 Webster]

   3. Those who are noble; the collective body of nobles or
      titled persons in a state; the aristocratic and patrician
      class; the peerage; as, the English nobility.
      [1913 Webster]

WordNet (r) 3.0 (2006):

nobility
    n 1: a privileged class holding hereditary titles [syn:
         nobility, aristocracy]
    2: the quality of elevation of mind and exaltation of character
       or ideals or conduct [syn: nobility, nobleness,
       magnanimousness, grandeur]
    3: the state of being of noble birth [syn: nobility,
       noblesse]

Moby Thesaurus II by Grady Ward, 1.0:

258 Moby Thesaurus words for "nobility":
   Babylonian splendor, FFVs, aedileship, ancienne noblesse,
   archbishopric, archiepiscopacy, archiepiscopate, aristocracy,
   assured probity, augustness, authority, baronage, baronetage,
   barons, bigheartedness, bigness, birth, bishopric, blamelessness,
   blue blood, brilliance, chairmanship, chancellery, chancellorate,
   chancellorship, character, chiefery, chiefry, chieftaincy,
   chieftainry, chieftainship, chivalrousness, chivalry, class,
   cleanness, consequence, conspicuousness, consulate, consulship,
   courtliness, cream, deanery, decency, dictatorship, dictature,
   dignifiedness, dignity, directorship, distinction, elaborateness,
   elect, elegance, elevation, elite, eminence, emirate, episcopacy,
   erectness, errantry, establishment, estimableness, ethics,
   exaltation, excellence, fairness, fame, generosity, generousness,
   glory, good character, goodness, gorgeousness, governorship,
   grandeur, grandiosity, grandness, gravity, great heart,
   greatheartedness, greatness, greatness of heart, haut monde,
   headship, hegemony, heroism, hierarchy, high ideals, high life,
   high mightiness, high principles, high society, high-mindedness,
   honesty, honor, honorableness, idealism, illustriousness,
   immaculacy, importance, imposingness, impressiveness, influence,
   integrity, irreproachability, irreproachableness, justice,
   justness, kingliness, knight-errantry, knightage, knightliness,
   largeheartedness, lavishness, leadership, liberality, liberalness,
   loftiness, lordliness, lords of creation, lordship, luxuriousness,
   luxury, magistracy, magistrateship, magistrature, magnanimity,
   magnanimousness, magnificence, majesty, mark, masterdom,
   mastership, mastery, mayoralty, mayorship, metropolitanate,
   metropolitanship, moral excellence, moral strength,
   noble-mindedness, nobleness, noblesse, noblesse de robe,
   notability, note, old nobility, openhandedness, outstandingness,
   overlapping, papacy, pashadom, pashalic, patriarchate, patriarchy,
   peerage, plushness, pontificality, pontificate, popedom, popehood,
   popeship, poshness, position, power elite, power structure,
   prefectship, prefecture, premiership, presidency, presidentship,
   prestige, pride of bearing, pride of place, primacy,
   prime-ministership, prime-ministry, princedom, princeliness,
   princeship, principality, principles, probity, proconsulate,
   proconsulship, prominence, protectorate, protectorship,
   proud bearing, proudness, provostry, provostship, pureness, purity,
   rank, rectitude, rectorate, rectorship, regality, regency,
   regentship, renown, reputability, respectability, resplendence,
   righteousness, ritziness, royalty, ruling circles, ruling class,
   sedateness, seigniory, seneschalship, seneschalsy, sheikhdom,
   sheriffalty, sheriffcy, sheriffdom, shrievalty, significance,
   sobriety, solemnity, splendidness, splendiferousness, splendor,
   stainlessness, state, stateliness, sublimity, sumptuousness,
   supereminence, supervisorship, suzerainship, suzerainty,
   the Establishment, the Four Hundred, the best, the best people,
   the brass, the classes, top people, tribunate, unimpeachability,
   unimpeachableness, unspottedness, upper class, upper classes,
   upper crust, upper ten, upper ten thousand, uppercut, uprightness,
   upstandingness, venerability, virtue, virtuousness, vizierate,
   viziership, worthiness