The most common and most likely answer to this crossword clue is the 9 letter word CLOUDIEST
I've seen this crossword clue in The Guardian
C
L
O
U
D
I
E
S
T
Buddy explains!
The straight part
We know that "Most unclear" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case most unclear = cloudiest.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 CLOUDIEST mean?
CLOUDIEST adjective- Covered with or characterised by clouds; overcast.
- Not transparent or clear.
- Uncertain; unclear.
- Using or relating to cloud computing.
- Shady; sketchy; suspicious