The most common and most likely answer to this crossword clue is the 8 letter word ABSTRUSE
I've seen this crossword clue in The Daily Telegraph
A
B
S
T
R
U
S
E
More clues leading to the result ABSTRUSE
- Busts are terribly hard to grasp
- Difficult to understand cruel treatment imprisoning three leaders of strike
- Hard to fathom good man getting right into obloquy
- Obscure university hospital’s third contribution to breast reconstruction
- Monstrously stab king, and profit? It’s hard to fathom
- Esoteric system for stopping the introduction of Tory stratagem
- Resistance on street to intervene in corrupt practice is difficult to understand
- Busts are being developed beyond comprehension
- Sailor stumped by stratagem hard to understand
- Hard to fathom why corruption engulfed good man and king
Buddy explains!
The straight part
We know that "Mysterious" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mysterious = abstruse.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 ABSTRUSE mean?
ABSTRUSE adjective- Difficult to comprehend or understand.
- Concealed or hidden out of the way; secret.