Deceit means deliberately making someone believe something false. When you practice deceit, you're lying or misleading people on purpose to trick them. A person might use deceit to hide something they've done wrong, or to gain something they don't deserve.

Deceit is different from an innocent mistake or misunderstanding. If you tell your friend the library closes at five o'clock because you honestly thought it did, but it actually closes at six, that's not deceit. That's just being wrong. But if you know the library closes at six and you tell your friend it closes at five because you want them to leave early, that's deceit. You're intentionally creating a false belief in their mind.

Deceitful people often seem trustworthy at first, which is part of how their deception works. They might smile and act friendly while secretly planning to cheat you. Stories and fables often feature deceitful characters like the fox who tricks the crow into dropping her cheese, or the wolf who disguises himself to fool Little Red Riding Hood.

The related word deception means the act of deceiving, while deceive is the verb form: to deceive someone means to use deceit against them. Once people discover you've been deceitful, they lose trust in you, and rebuilding that trust becomes incredibly difficult.