The Collaborative International Dictionary of English v.0.48:

Classic \Clas"sic\ (kl[a^]s"s[i^]k), Classical \Clas"sic*al\, a.
   [L. classicus relating to the classes of the Roman people,
   and especially to the frist class; hence, of the first rank,
   superior, from classis class: cf. F. classique. See Class,
   n.]
   1. Of or relating to the first class or rank, especially in
      literature or art.
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            Give, as thy last memorial to the age,
            One classic drama, and reform the stage. --Byron.
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            Mr. Greaves may justly be reckoned a classical
            author on this subject [Roman weights and coins].
                                                  --Arbuthnot.
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   2. Of or pertaining to the ancient Greeks and Romans, esp. to
      Greek or Roman authors of the highest rank, or of the
      period when their best literature was produced; of or
      pertaining to places inhabited by the ancient Greeks and
      Romans, or rendered famous by their deeds.
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            Though throned midst Latium's classic plains. --Mrs.
                                                  Hemans.
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            The epithet classical, as applied to ancient
            authors, is determined less by the purity of their
            style than by the period at which they wrote.
                                                  --Brande & C.
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            He [Atterbury] directed the classical studies of the
            undergraduates of his college.        --Macaulay.
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   3. Conforming to the best authority in literature and art;
      chaste; pure; refined; as, a classical style.
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            Classical, provincial, and national synods.
                                                  --Macaulay.
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   Classicals orders. (Arch.) See under Order.
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WordNet (r) 3.0 (2006):

classical
    adj 1: of or relating to the most highly developed stage of an
           earlier civilisation and its culture; "classic Cinese
           pottery" [syn: classical, classic] [ant:
           nonclassical]
    2: of recognized authority or excellence; "the definitive work
       on Greece"; "classical methods of navigation" [syn:
       authoritative, classical, classic, definitive]
    3: of or relating to the study of the literary works of ancient
       Greece and Rome; " a classical scholar"
    4: (language) having the form used by ancient standard authors;
       "classical Greek
    5: of or pertaining to or characteristic of the ancient Greek
       and Roman cultures; "classical mythology"; "classical [syn:
       classical, classic, Greco-Roman, Graeco-Roman,
       Hellenic]
    n 1: traditional genre of music conforming to an established
         form and appealing to critical interest and developed
         musical taste [syn: classical music, classical,
         serious music]

Moby Thesaurus II by Grady Ward, 1.0:

157 Moby Thesaurus words for "classical":
   Attic, Ciceronian, Gothic, Greek, Latin, Roman, Victorian,
   absolute, aesthetic, antediluvian, antiquated, antique, archaic,
   archetypical, arrant, artistic, authoritative, belletristic,
   capital, champion, chaste, choice, classic, clear, common,
   commonplace, complete, consummate, crass, decided, definitive,
   developed, direct, downright, easy, egregious, elegant,
   established, everyday, excellent, exemplary, expert, famous, fine,
   finished, flagrant, fossil, fossilized, fully developed, garden,
   garden-variety, glaring, graceful, gracile, gross, grown old,
   homely, homespun, household, ideal, in good taste, influential,
   intolerable, limpid, literary, lucid, masterful, masterly,
   matter-of-fact, mature, matured, medieval, mid-Victorian, model,
   natural, neat, nondescript, of choice, of other times, of quality,
   old-world, ordinary, out-and-out, outright, paradigmatic, pellucid,
   perfect, perfected, perspicuous, petrified, plain, pleasing,
   polished, positive, precedential, precious, prime, proficient,
   profound, pronounced, proper, prosaic, prosy, prototypal, pure,
   pure and simple, quiet, quintessential, rank, refined, regular,
   representative, restrained, ripe, ripened, round, serious,
   shattering, shocking, simple, standard, stark, stark-staring,
   straightforward, subdued, superannuated, superior, superlative,
   surpassing, tasteful, terse, the veriest, thorough, thoroughgoing,
   top, top-notch, total, traditional, trim, typical, unaffected,
   unbearable, unconscionable, undeniable, understated, unequivocal,
   unlabored, unmitigated, unobtrusive, unqualified, unrelieved,
   unspoiled, utter, weighty, well-chosen, workaday, workday