The most common and most likely answer to this crossword clue is the 9 letter word MEGABUCKS
I've seen this crossword clue in The Daily Telegraph
M
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A
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More clues leading to the result MEGABUCKS
- Be getting on motorway over part of England to make fortune
- A packet young men found under a stone, lifted up
- County after game to fix for a lot of money
- After lifting of a masterpiece, dashing chaps making lots of cash
- Upturned stone with top marking young man’s pile of money?
- Much money mother hoards say, somewhere north of Greater London
- County after game generating huge wads of cash?
- Loadsamoney cameo sent up a little English county
- Beckham messed up rejecting Hearts for good — and United — then succeeded, making a fortune
- Processed game and deer making lots and lots of money
Buddy explains!

The straight part
We know that "huge sum of money" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case huge sum of money = megabucks.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 MEGABUCKS mean?
MEGABUCKS noun- A million dollars.