The most common and most likely answer to this crossword clue is the 9 letter word INSIDIOUS
I've seen this crossword clue in The Daily Telegraph
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More clues leading to the result INSIDIOUS
- Devious, doing time, endless debts to pay
- One with common sense skirts two-thirds of railway track — potentially harmful
- Short position with private knowledge, obtaining debt pledges – sneaky!
- Treacherous and in debt, son lies about phony IDs
- Home investor in British Gas covers debts advancing gradually
Buddy explains!

The straight part
We know that "Devious" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case devious = insidious.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 INSIDIOUS mean?
INSIDIOUS adjective- Producing harm in a stealthy, often gradual, manner.
- Intending to entrap; alluring but harmful.
- Treacherous.