See classic § Etymology for history. By surface analysis, class +‎ -ical = classic + -al

• IPA: /ˈklæsɪkl̩/

classical

1. Of or relating to the first class or rank, especially in literature or art.
   • 1727, John Arbuthnot, Tables of Ancient Coins, Weights and Measures Explain'd and Exemplify'd in Several Dissertations ↗, page 15:

     ... Mr. Greaves, who may be juſtly reckoned a Claſſical Author on this Subject.

2. Of or pertaining to established principles in a discipline.
   • 1992, Rudolf M[athias] Schuster, The Hepaticae and Anthocerotae of North America: East of the Hundredth Meridian, volume V, Chicago, Ill.: Field Museum of Natural History, →ISBN, page vii:

     Herbarium material does not, indeed, allow one to extrapolate safely: what you see is what you get; what you get is classical alpha-taxonomy which is, very largely and for sound reasons, in disrepute today.

3. (music) Describing Western music and musicians of the late 18th and early 19th centuries.
4. (informal, music) Describing art music (rather than pop, jazz, blues, etc), especially when played using instruments of the orchestra.
5. Of or pertaining to the ancient Greeks and Romans, especially 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.
   • 1853, Thomas Babington Macaulay, "Francis Atterbury" in Encyclopædia Britannica (8th ed.). Dated through The Miscellaneous Writings and Speeches of Lord Macaulay, page 344 ↗

     He [Atterbury] directed the classical studies of the undergraduates of his college.

6. Knowledgeable or skilled in the classics; versed in the classics.

   a classical scholar

7. Conforming to the best authority in literature and art; chaste; pure; refined

   classical dance.

   • 1848, Thomas Babington Macaulay, The History of England from the Accession of James the Second, volume 1, page 151.

     Classical, provincial, and national synods.

8. (physics) Pertaining to models of physical laws that do not take quantum or relativistic effects into account; Newtonian or Maxwellian.

   Antonyms: quantum, relativistic

• classic (see Usage notes regarding differentiation.)

• French: classique
• German: klassisch
• Italian: classico
• Portuguese: clássico
• Russian: класси́ческий
• Spanish: clásico

• German: klassisch

• French: classique
• German: klassisch
• Italian: classico
• Portuguese: clássico
• Russian: класси́ческий
• Spanish: clásico

• French: classique
• German: klassisch
• Italian: classico
• Portuguese: clássico
• Russian: класси́ческий
• Spanish: clásico

classical

1. (countable) One that is classical in some way; for example, a classical economist.
2. Short for classical music.
3. (chess) Short for classical chess.