The most common and most likely answer to this crossword clue is the 8 letter word TEXTBOOK
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Buddy explains!
The straight part
We know that "Classic" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case classic = textbook.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TEXTBOOK mean?
TEXTBOOK noun- A coursebook, a formal manual of instruction in a specific subject, especially one for use in schools or colleges.
- Of or pertaining to textbooks or their style, especially in being dry and pedagogical; textbooky, textbooklike.
- Having the typical characteristics of some class of phenomenon, so that it might be included as an example in a textbook.