The most common and most likely answer to this crossword clue is the 9 letter word DASTARDLY
D
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More clues leading to the result DASTARDLY
- Playing darts, lady is mean and wicked!
- Diabolical day Donald Trump starts salary ‘enhancement’
- Despicable pop star found inside with lolly wrapper
- He could be a tad sly hogging road
- Team's outstanding player goes onto Disabled List. It's all in a day, but really low
- Underhanded prosecutor's appeal ultimately entered late
Buddy explains!

The straight part
We know that "diabolical" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case diabolical = dastardly.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 DASTARDLY mean?
DASTARDLY adjective- In the manner of a dastard; marked by cowardice; pusillanimous
- Treacherous; given to backstabbing
- In a cowardly or treacherous fashion.