The most common and most likely answer to this crossword clue is the 5 letter word TOUGH
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The straight part
We know that "unlucky" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unlucky = tough.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 TOUGH mean?
TOUGH noun- A person who obtains things by force; a thug or bully.
- To endure.
- To toughen.
- Strong and resilient; sturdy.
- (of food) Difficult to cut or chew.
- Rugged or physically hardy.
- Stubborn.
- (of weather etc) Harsh or severe.
- Rowdy or rough.
- (of questions, etc.) Difficult or demanding.
- Undergoing plastic deformation before breaking.
- Used to indicate lack of sympathy