Why is the ninth month called September?
1610s, "of the highest class; approved as a model," from French classique (17c.), from Latin classicus "relating to the (highest) classes of the Roman people," hence, "superior," from classis (see class). Originally in English, "of the first class;" meaning "belonging to standard authors of Greek and Roman antiquity" is attested from 1620s.
"a Greek or Roman writer or work," 1711, from classic (adj.). So, by mid-19c., any work in any context held to have a similar quality or relationship. In classical Latin noun use of classicus meant "a Marine" (miles classicus) from the "military division" sense of classis.
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.