The most common and most likely answer to this crossword clue is the 10 letter word FENESTRATE
I've seen this crossword clue in Financial Times
F
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N
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S
T
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A
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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 FENESTRATE mean?
FENESTRATE noun- Any extinct bryozoan in the order Fenestrida (also known as Fenestrata).
- To cut an opening into.
- Fenestrated
- Having numerous openings; irregularly reticulated.
- Having transparent spots, like the wings of certain butterflies.