The most common and most likely answer to this crossword clue is the 5 letter word LATIN
I've seen this crossword clue in Financial Times
L
A
T
I
N
More clues leading to the result LATIN
- Incompletely translating ancient language
- Ancient language the French can identify
- Language the French can put together
- Old tongue preserved in gelatine
- Language seen in loo left by King and Earl
- Muscle linked to hip or tongue
- Mexican from city with money
- Language used by lousy leader ain’t working
- A classic in Italian, somewhat making a comeback?
- Oddly picked least popular school subject
Buddy explains!
The straight part
We know that "A classic" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a classic = latin.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.