Noah Webster's New International Dictionary of the English Language

1. (v.) To make bright or brighter; to make to shine; to increase the luster of; to give a brighter hue to.

2. (v.) To make illustrious, or more distinguished; to add luster or splendor to.

3. (v.) To improve or relieve by dispelling gloom or removing that which obscures and darkens; to shed light upon; to make cheerful; as, to brighten one's prospects.

4. (v.) To make acute or witty; to enliven.

5. (v. i.) To grow bright, or more bright; to become less dark or gloomy; to clear up; to become bright or cheerful.