The most common and most likely answer to this crossword clue is the 9 letter word NOTOCHORD
I've seen this crossword clue in The Daily Telegraph
N
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T
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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 NOTOCHORD mean?
NOTOCHORD noun- A flexible rodlike structure that forms the main support of the body in the lowest chordates; a primitive spine
- A similar structure found in the embryos of vertebrates from which the spine develops