Assurance is a feeling of confidence and certainty about something. When you have assurance, you feel secure that things will work out the way you expect or hope. A pilot might speak with assurance about landing safely in bad weather because of her training and experience. A friend might give you assurance that she'll be there to support you, making you feel certain you can count on her.

The word often appears in phrases like “words of assurance” or “self-assurance.” When someone speaks with assurance, they sound confident and sure of what they're saying. Self-assurance means having confidence in your own abilities and judgment, like feeling assured you can solve a difficult math problem because you've practiced similar ones before.

Assurance can also mean a promise or guarantee that something will happen. An insurance company provides assurance that they'll help if something goes wrong. A teacher might give students assurance that hard work will improve their grades.

Notice how assurance differs from arrogance: assured people have genuine confidence based on knowledge or experience, while arrogant people act superior without good reason. When you study thoroughly for a test, you might feel a quiet assurance that you're prepared. That's completely different from bragging or showing off.