The most common and most likely answer to this crossword clue is the 11 letter word TRANSLUCENT
I've seen this crossword clue in The Daily Telegraph
T
R
A
N
S
L
U
C
E
N
T
More clues leading to the result TRANSLUCENT
Buddy explains!

The straight part
We know that "Clear" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case clear = translucent.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 TRANSLUCENT mean?
TRANSLUCENT adjective- Allowing light to pass through, but diffusing it.
- Clear, lucid, or transparent.