Untruthfulness is the quality of being dishonest or not telling the truth. When someone speaks with untruthfulness, they're deliberately saying things they know aren't true, whether through lies, deception, or leaving out important facts.

Untruthfulness goes beyond simply being wrong about something. If you think your friend's birthday is next Tuesday when it's actually next Wednesday, that's a mistake, not untruthfulness. But if you tell your parents you finished your homework when you actually haven't touched it, that's untruthfulness: you know the real situation and chose to misrepresent it.

People practice untruthfulness for many reasons. Sometimes they're trying to avoid consequences, like a student who lies about breaking a window. Sometimes they want something they don't deserve, like an athlete who lies about their age to compete in a younger division. Sometimes they simply want to look better than they are.

The opposite of untruthfulness is truthfulness or honesty. A person known for untruthfulness gradually loses the trust of others. Even when they do tell the truth, people may wonder if they're being deceived.