The most common and most likely answer to this crossword clue is the 11 letter word QUADRILLION
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The straight part
We know that "number" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case number = quadrillion.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 QUADRILLION mean?
QUADRILLION noun- Any very large number, exceeding normal description.
- (modern British and Australian, short scale) A thousand trillion (logic: 1,000 × 1,000^4): 1 followed by fifteen zeros, 1015.
- (long scale) A million trillion (logic: 1,000 × 1,000,000^2): 1 followed by twenty-four zeros, 1024.