The most common and most likely answer to this crossword clue is the 7 letter word BILLION
I've seen this crossword clue in The Guardian
B
I
L
L
I
O
N
More clues leading to the result BILLION
Buddy explains!
The straight part
We know that "Large number" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case large number = billion.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 BILLION mean?
BILLION noun- (modern British & Australian, short scale) a thousand million (logic: 1,000 × 1,000^2): 1 followed by nine zeros, 109; a milliard
- (British & Australian, long scale) A million million (logic: 1,000,000^2): a 1 followed by twelve zeros; 1012
- An unspecified very large number.