The most common and most likely answer to this crossword clue is the 8 letter word VALERIAN
I've seen this crossword clue in Independent
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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 VALERIAN mean?
VALERIAN noun- A hardy perennial flowering plant, Valeriana officinalis, with heads of sweetly scented pink or white flowers.
- More generally, any plant of the genus Valeriana.
- The root of Valeriana officinalis, used in herbal medicine.
- An extract of the dried roots of the Valeriana officinalis used in herbal medicine as a sedative.