The most common and most likely answer to this crossword clue is the 8 letter word ATARAXIA
I've seen this crossword clue in Financial Times
A
T
A
R
A
X
I
A
Buddy explains!

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 ATARAXIA mean?
ATARAXIA noun- Tranquility of mind; absence of mental disturbance.