The most common and most likely answer to this crossword clue is the 8 letter word CANTRAIL
I've seen this crossword clue in Financial Times
C
A
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T
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Buddy explains!

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 CANTRAIL mean?
CANTRAIL noun- A length of metal (earlier timber) supporting the outer edge of the roof of a railway carriage; also found on locomotives, buses and coaches.