The most common and most likely answer to this crossword clue is the 6 letter word NAUGHT
I've seen this crossword clue in The Guardian
N
A
U
G
H
T
More clues leading to the result NAUGHT
Buddy explains!

The straight part
We know that "Nothing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case nothing = naught.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 NAUGHT mean?
NAUGHT noun- Nothingness.
- (old-fashioned) Alternative spelling of nought
- Nothing.
- Nothing; something which does not exist.
- A thing or person of no worth or value; nil.
- Not any quantity of number; zero; the score of no points in a game.
- The figure or character representing, or having the shape of, zero.