A believer is someone who accepts something as true, especially when it can't be completely proven. Most commonly, a believer is a person who has faith in God or follows a particular religion. Christians, Muslims, Jews, Hindus, and members of other faiths are all believers in their respective traditions.

The word isn't limited to religion, though. You might be a believer in hard work, meaning you're convinced that effort and persistence lead to success. A scientist might be a believer in a new theory she's developing, trusting her research even before she has all the evidence. When a coach says “I'm a believer in this team,” he means he has confidence in their ability to win.

Being a believer often means staying committed to something even when others doubt it or when proof is incomplete. It takes a kind of courage: believers choose to trust in something larger than what they can see or touch. The opposite would be a skeptic or doubter, someone who questions or refuses to accept something without solid proof.

The phrase “I'm a believer” usually means someone has become convinced of something they once doubted. Maybe they didn't think practice mattered until they saw their own skills improve, and now they're believers in the power of repetition.