The most common and most likely answer to this crossword clue is the 9 letter word UNSAVOURY
U
N
S
A
V
O
U
R
Y
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The straight part
We know that "Nasty" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case nasty = unsavoury.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 UNSAVOURY mean?
UNSAVOURY adjective- Not savory; without flavor.
- Of bad taste; distasteful.
- Making an activity undesirable.
- Disreputable, not respectable, of questionable moral character.