The most common and most likely answer to this crossword clue is the 8 letter word MEGALITH
I've seen this crossword clue in The Daily Telegraph
M
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Buddy explains!

The straight part
We know that "huge stone" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case huge stone = megalith.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 MEGALITH mean?
MEGALITH noun- A construction involving one or several roughly hewn stone slabs of great size.
- A large stone used in such a construction.