The most common and most likely answer to this crossword clue is the 10 letter word MUSHROOMED
I've seen this crossword clue in Financial Times
M
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S
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M
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More clues leading to the result MUSHROOMED
Buddy explains!
The straight part
We know that "grew rapidly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case grew rapidly = mushroomed.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 MUSHROOMED mean?
MUSHROOMED verb- To grow quickly to a large size.
- To gather mushrooms.
- To form the shape of a mushroom.