The most common and most likely answer to this crossword clue is the 8 letter word CAROTENE
I've seen this crossword clue in The Guardian
C
A
R
O
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.
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What does CAROTENE mean?
CAROTENE noun- A class of tetraterpene plant pigments; they vary in colour from yellow, through orange to red, this colour originating in a chain of alternating single and double bonds.
- Specifically, a number of isomers of tetraterpene hydrocarbons, C40H56, (especially beta-carotene), present in carrots etc, which are converted into vitamin A in the liver.