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.
      [1913 Webster]

            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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The Collaborative International Dictionary of English v.0.48:

Classic \Clas"sic\, n.
   1. A work of acknowledged excellence and authority, or its
      author; -- originally used of Greek and Latin works or
      authors, but now applied to authors and works of a like
      character in any language.
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            In is once raised him to the rank of a legitimate
            English classic.                      --Macaulay.
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   2. One learned in the literature of Greece and Rome, or a
      student of classical literature.
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WordNet (r) 3.0 (2006):

classic
    adj 1: of recognized authority or excellence; "the definitive
           work on Greece"; "classical methods of navigation" [syn:
           authoritative, classical, classic, definitive]
    2: of or relating to the most highly developed stage of an
       earlier civilisation and its culture; "classic Cinese
       pottery" [syn: classical, classic] [ant: nonclassical]
    3: 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: a creation of the highest excellence
    2: an artist who has created classic works

The Free On-line Dictionary of Computing (19 January 2023):

classic

    An adjective used before or after a noun to describe
   the original version of something, especially if the original
   is considered to be better.

   Examples include "Star Trek Classic" - the original TV series
   as opposed to the films, ST The Next Generation or any of the
   other spin-offs and follow-ups; or "PC Classic" - IBM's
   ISA-bus computers as opposed to the PS/2 series.

   (1996-10-27)