Naught means nothing or zero. When someone's careful plans come to naught, they fail completely and produce nothing. If you work hard on a sandcastle and a wave washes it away, your effort has come to naught.

The word appears most often in older books and formal writing. In The Lord of the Rings, Gandalf warns that “all our labors will be for naught” if they fail, meaning everything they've worked for will amount to nothing. You might also see it in the phrase all for naught, which means “all for nothing.”

In British English, naught can also mean the number zero, similar to how Americans sometimes say “oh” when reading out numbers. Someone might say “naught point five” for 0.5.

The word naughty comes from the same root. Originally, a naughty child was described as having naught (nothing), though now it just means mildly misbehaving.