classic adj.

c. 1600, "group of students," in U.S. especially "number of pupils in a school or college of the same grade," from French classe (14c.), from Latin classis "a class, a division; army, fleet," especially "any one of the six orders into which Servius Tullius divided the Roman people for the purpose of taxation;" traditionally originally "the people of Rome under arms" (a sense attested in English from 1650s), and thus akin to calare "to call (to arms)," from PIE root *kele- (2) "to shout." In early use in English also in Latin form classis.

Meaning "an order or rank of persons, a number of persons having certain characteristics in common" is from 1660s. School and university sense of "course, lecture" (1650s) is from the notion of a form or lecture reserved to scholars who had attained a certain level. Natural history sense "group of related plants or animals" is from 1753. Meaning "high quality" is from 1874. Meaning "a division of society according to status" (with upper, lower, etc.) is from 1763. Class-consciousness (1903) is from German Klassenbewusst.

The fault, the evil, in a society is when privilege exists without responsibility and duty. The evil of the classless society is that it tends to equalize the responsibility, to atomize it into responsibility of the whole population—and therefore everyone becomes equally irresponsible. [T.S. Eliot, BBC interview with Leslie Paul, 1958]

1590s, "of the highest rank" (originally in literature), from classic + -al (1). Classical music (1836) was defined originally against romantic music.

[I]n general, as now used, the term classical includes the composers active in instrumental music from somewhere about 1700 to say 1830. Hence the list includes among the great names those of Bach, his sons, Haydn, Mozart, Beethoven, Clementi, Dussek, Pleyel, Cramer, etc. The next step beyond the term classical is "modern romantic," the composers of which school may be taken to include all the writers for pianoforte from about 1829 (when Mendelssohn published the first "Songs without Words") down to the present. The term romantic in this sense means strongly marked, extraordinary, intending to tell stories and the like. ["Music, Its Ideals and Methods," W.S.B. Mathews, 1897]

But already by 1880s it was acknowledged the term had a double sense: Music that had withstood the test of time, as well as music of a style contrasted to "romantic." Later (early 20c.) it was contrasted to jazz (in this sense more often with reference to the orchestras than to the music itself). Still later it stood in contrast to popular music generally (mid-20c.). Classical history is the history of ancient Greece and Rome; ancient history is the history of mankind from the earliest reliable records to the fall of Rome (476 C.E.). Related: Classically.