1.Definition: (of language) transparently clear; easily understandable
"Lucid directions", "Pellucid prose"
2.Definition: capable of thinking and expressing yourself in a clear and consistent manner
"A lucid thinker"
3.Definition: having a clear mind
"A lucid moment in his madness"
4.Definition: transmitting light; able to be seen through with clarity
"Lucid air", "A pellucid brook"