The most common and most likely answer to this crossword clue is the 11 letter word ALTOSTRATUS
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More clues leading to the result ALTOSTRATUS
Buddy explains!
The straight part
We know that "Cloud" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cloud = altostratus.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 ALTOSTRATUS mean?
ALTOSTRATUS noun- A principal medium-level cloud type in the form of a gray or bluish (never white) sheet or layer of striated, fibrous, or uniform appearance.