An untruth is a statement that isn't true. It's a formal way to describe something false that someone says.

Unlike a simple mistake where you accidentally get a fact wrong, untruth can suggest the speaker knows better. If a student tells their teacher “I turned in my homework” when they actually didn't, that's an untruth. If a witness in court says “I didn't see anything” when they really did, that's also an untruth.

The word sounds more polite and indirect than saying someone “lied,” which is why adults sometimes choose it in formal situations. A politician might accuse another of “spreading untruths” rather than directly calling them a liar. A book reviewer might say an author's claim contains “several untruths” instead of saying the author is lying.

Notice that untruth can describe both the act of saying something false and the false statement itself. You might say “she told an untruth” or “that story contains many untruths.” Either way, the word points to the gap between what someone says and what's actually real.