The most common and most likely answer to this crossword clue is the 7 letter word CUMULUS
I've seen this crossword clue in Independent
C
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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 CUMULUS mean?
CUMULUS noun- A large white puffy cloud that develops through convection. On a hot, humid day, they can form towers and even become cumulonimbus clouds.
- A mound or heap.