The Collaborative International Dictionary of English v.0.48:

Peerage \Peer"age\, n. [See Peer an equal, and cf. Parage.]
   1. The rank or dignity of a peer. --Blackstone.
      [1913 Webster]

   2. The body of peers; the nobility, collectively.
      [1913 Webster]

            When Charlemain with all his peerage fell. --Milton.
      [1913 Webster]

WordNet (r) 3.0 (2006):

peerage
    n 1: the peers of a kingdom considered as a group [syn:
         peerage, baronage]

Moby Thesaurus II by Grady Ward, 1.0:

24 Moby Thesaurus words for "peerage":
   FFVs, ancienne noblesse, aristocracy, baronage, baronetage,
   chivalry, elect, elite, haut monde, high life, high society,
   knightage, nobility, noblesse, noblesse de robe, old nobility,
   royalty, the Four Hundred, the classes, upper classes, upper crust,
   upper ten, upper ten thousand, uppercut