Sanguine means optimistic or positive, especially about how things will turn out. A sanguine person faces challenges with confidence and expects good results. If you're sanguine about an upcoming spelling bee, you believe you'll do well even though you know it will be tough.

The word comes from an old medical theory that linked personality to bodily fluids. Doctors once thought that people with lots of blood (Latin: sanguis) were naturally cheerful and hopeful. While that theory was wrong, the word stuck around to describe people with sunny dispositions.

Someone sanguine about their team's chances believes they'll win despite being the underdogs. A sanguine scientist keeps experimenting even after failures because she trusts she'll eventually solve the problem. This isn't foolish hope or ignoring reality: sanguine people see the obstacles clearly but maintain confidence that things will work out.

You might hear someone described as having a sanguine temperament, meaning they naturally tend toward hopefulness rather than worry. When a friend stays sanguine despite setbacks, they're focusing on possibilities rather than problems. Being sanguine doesn't guarantee success, but it can help people persist long enough to achieve it.