Lucid

Adjective:

1. (of language) transparently clear; easily understandable
(Usage: Lucid directions)

2. Having a clear mind
(Usage: A lucid moment in his madness)

3. Capable of thinking and expressing yourself in a clear and consistent manner
(Usage: A lucid thinker)

4. Transmitting light; able to be seen through with clarity
(Usage: Lucid air)

Synonyms:

1. Coherent
2. Crystal Clear
3. Crystalline
4. Limpid
5. Logical
6. Luculent
7. Pellucid
8. Perspicuous
9. Transparent