The most common and most likely answer to this crossword clue is the 8 letter word WHACKING
I've seen this crossword clue in The Daily Telegraph
W
H
A
C
K
I
N
G
More clues leading to the result WHACKING
Buddy explains!

The straight part
We know that "Very large" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case very large = whacking.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 WHACKING mean?
WHACKING verb- To hit, slap or strike.
- To kill, bump off.
- To share or parcel out; often with up.
- To beat convincingly; to thrash.
- (usually in the negative) To surpass; to better.
- A beating.
- Exceptionally large; whopping (often followed by an adjective such as great or big).