The most common and most likely answer to this crossword clue is the 9 letter word TETRAGONS
I've seen this crossword clue in The Daily Telegraph
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More clues leading to the result TETRAGONS
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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 TETRAGONS mean?
TETRAGONS noun- Quadrilateral.
- An aspect of two planets with regard to the Earth when they are distant from each other ninety degrees, or a quarter-circle.