The most common and most likely answer to this crossword clue is the 9 letter word INEFFABLE
I've seen this crossword clue in Financial Times
I
N
E
F
F
A
B
L
E
More clues leading to the result INEFFABLE
- Fine comic story, so good I can’t tell you
- . Fiancée regularly skipped introduction to fairy tale – beyond words!
- Translation of fine story beyond description
- Geoff oddly ignored during ridiculous life ban – it’s beyond words
- Expert supports popular euphemism for swearword that’s not to be uttered
- Spinning fine yarn that’s beyond words
- Fine fable curiously inexpressible
- Energy forces inhabit Blaine magic? It’s beyond words
- Fine novel with story that’s unutterably great
- Fine rendition, story is too sacred to be uttered
Buddy explains!
The straight part
We know that "not to be mentioned" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not to be mentioned = ineffable.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 INEFFABLE mean?
INEFFABLE adjective- Beyond expression in words; unspeakable.
- Forbidden to be uttered; taboo.