brighten

American Heritage® Dictionary of the English Language, Fourth Edition

1. v. To make or become bright or brighter.

Century Dictionary and Cyclopedia

1. To grow bright or more bright; become less dark or gloomy: literally or figuratively.
2. To make bright or brighter in any manner; shed light on; make to shine; increase the luster of.
3. To dispel gloom from; cheer; make gay or cheerful: as, to brighten prospects.
4. To make illustrious or more distinguished; heighten the splendor of; add luster to.
5. To make acute or witty; sharpen the faculties of.
6. To add brilliancy to the colors of (prints, etc.), by boiling them in a solution of soda.

Wiktionary

1. v. transitive To make bright or brighter in color
2. v. transitive To add luster or splendor to
3. v. transitive (figuratively) To make more cheerful and pleasant; to enliven
4. v. intransitive To grow bright, or more bright in color; to clear up
5. v. intransitive To become brighter or more cheerful in mood

GNU Webster's 1913

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.
4. v. To make acute or witty; to enliven.
5. v. To grow bright, or more bright; to become less dark or gloomy; to clear up; to become bright or cheerful.

WordNet 3.0

1. v. become clear
2. v. make lighter or brighter