The most common and most likely answer to this crossword clue is the 9 letter word VERMILION
I've seen this crossword clue in Independent
V
E
R
M
I
L
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O
N
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The straight part
We know that "scarlet" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case scarlet = vermilion.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 VERMILION mean?
VERMILION noun- A vivid red synthetic pigment made of mercury sulfide.
- A bright orange-red colour.
- A type of red dye worn in the parting of the hair by married Hindu women.
- The red skin of the lips or its border with the skin of the face.
- The kermes or cochineal insect.
- The cochineal dye made from this insect.
- To color or paint vermilion.
- Having a brilliant red colour.
- Having the color of the vermilion dye.