The most common and most likely answer to this crossword clue is the 9 letter word LIQUORICE
I've seen this crossword clue in Financial Times
L
I
Q
U
O
R
I
C
E
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The straight part
We know that "Sweet" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sweet = liquorice.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 LIQUORICE mean?
LIQUORICE noun- The plant Glycyrrhiza glabra, or sometimes in North America the related American Licorice plant Glycyrrhiza lepidota.
- A type of candy made from that plant's dried root or its extract.
- A black colour, named after the licorice.
- A flavouring agent made from dried root portions of the aforementioned plant.