classic, classical

As adjectives, these words are partly interchangeable.

Nevertheless, classic should be used when the meaning is “a famous or supreme example of its type”:

• It was a classic case of mistaken identity.

Classical is preferred in reference to ancient Greek and Roman culture or to any music composed in a traditional, serious style:

• The Colosseum is an excellent example of classical Roman architecture.
• He was an outstanding performer of classical Hindu music.