Cryptic crossword clue
As Adam has pointed out, a cornel is a cherry tree genus Cornus

The most common and most likely answer to this crossword clue is the 1 plus 11 letter word 3 METRO/COVEY

I've seen this crossword clue in The Guardian
3
M
E
T
R
O
/
C
O
V
E
Y

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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.

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