The most common and most likely answer to this crossword clue is the 6 letter word NAUSEA
I've seen this crossword clue in Independent
N
A
U
S
E
A
More clues leading to the result NAUSEA
- Note a benefit supplied by a sickness
- What comes in waves after an upset tum, inside?
- Greek character admitting a deep malaise
- Aversion is new treatment in Alcoholics Anonymous
- Greek character boxing a marine shows revulsion
- European in sauna developed sickness
- A turn in northern waters?
- Noisily chews kebab regularly causing feelings of revulsion
- Sodium securing a purpose — disgust?
- Revulsion has a benefit in North America
Buddy explains!

The straight part
We know that "sickness" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sickness = nausea.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 NAUSEA mean?
NAUSEA noun- A feeling of illness or discomfort in the digestive system, usually characterized by a strong urge to vomit.
- Strong dislike or disgust.
- Motion sickness.