The most common and most likely answer to this crossword clue is the 8 letter word DISEASED
I've seen this crossword clue in The Times
D
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S
E
A
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D
More clues leading to the result DISEASED
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The straight part
We know that "Australian crook" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case australian crook = diseased.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 DISEASED mean?
DISEASED verb- To cause unease; to annoy, irritate.
- To infect with a disease.
- Affected with or suffering from disease.