* Lucid: Clear, easy to understand, bright.
* Lucidity: Clearness, intelligibility, brightness.
* Luculent: Shining, bright, clear.
* Lucubrate: To study or work late into the night.
* Lucrative: Profitable, financially rewarding.
* Lucifer: The light-bringer, a name for the devil.
The root "luc" comes from the Latin word "lux", meaning "light".