The Collaborative International Dictionary of English v.0.48:

Peerless \Peer"less\, a.
   Having no peer or equal; matchless; superlative. "Her
   peerless feature." --Shak.
   [1913 Webster]

         Unvailed her peerless light.             --Milton.
   [1913 Webster] --Peer"less*ly, adv. -- Peer"less*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

peerless
    adj 1: eminent beyond or above comparison; "matchless beauty";
           "the team's nonpareil center fielder"; "she's one girl in
           a million"; "the one and only Muhammad Ali"; "a peerless
           scholar"; "infamy unmatched in the Western world"; "wrote
           with unmatchable clarity"; "unrivaled mastery of her art"
           [syn: matchless, nonpareil, one(a), one and
           only(a), peerless, unmatched, unmatchable,
           unrivaled, unrivalled]

Moby Thesaurus II by Grady Ward, 1.0:

84 Moby Thesaurus words for "peerless":
   absolute, best, beyond all praise, beyond compare,
   beyond comparison, champion, chaste, choice, consummate,
   defectless, easily first, elect, elite, excellent, facile princeps,
   faultless, finest, flawless, for the best, greatest, handpicked,
   ideal, immaculate, immortal, impeccable, incomparable,
   indefectible, indefective, infallible, inimitable, invincible,
   irreproachable, just right, matchless, ne plus ultra, nonpareil,
   nulli secundus, optimal, optimum, paramount, perfect, picked,
   prime, prize, pure, quintessential, second to none, select,
   sinless, sovereign, spotless, stainless, sui generis, superb,
   superior, superlative, supreme, surpassing, taintless,
   unadulterated, unapproachable, unapproached, unbeatable,
   unblemished, uncontaminated, unequaled, unexampled, unexcelled,
   unfaultable, unique, unmatchable, unmatched, unmixed, unparagoned,
   unparalleled, unpeered, unrivaled, unspotted, unsurpassable,
   unsurpassed, untainted, very best, without equal,
   without parallel