Lucid (adjective)

1. Easily understood; clear and coherent.
2. Mentally clear; able to think, reason, or remember normal.
3. Of a person, having a clear mind, particularly in the context of a medical condition.

Origin:

Late middle english: from latin lucidus "light, clear, bright", from lux, luc- "light".

Examples:

1. The lucid explanation made the concept easy to understand.
2. The lucid writing style made the book easy to read.
3. The lucid argument was convincing.
4. The lucid dreamer was aware that they were dreaming.
5. The lucid patient was able to communicate their needs.