The most common and most likely answer to this crossword clue is the 9 letter word ARTERIOLE
I've seen this crossword clue in The Daily Telegraph
A
R
T
E
R
I
O
L
E
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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 ARTERIOLE mean?
ARTERIOLE noun- One of the small branches of an artery, especially one that connects with capillaries.