The most common and most likely answer to this crossword clue is the 10 letter word INVIOLABLE
I've seen this crossword clue in Financial Times
I
N
V
I
O
L
A
B
L
E
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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 INVIOLABLE mean?
INVIOLABLE adjective- Not violable; not to be infringed.
- Not susceptible to violence, or of being profaned, corrupted, or dishonoured.
- Incapable of being injured or invaded; indestructible.