lucid
adjective(lu-cid)
(of language) transparently clear; easily understandable
Examples:
Lucid directions. 
Pellucid prose. 
lucid
adjective(lu-cid)
transmitting light; able to be seen through with clarity
Examples:
Lucid air. 
A pellucid brook. 
lucid
adjective(lu-cid)
capable of thinking and expressing yourself in a clear and consistent manner
Examples:
A lucid thinker. 
lucid
adjective(lu-cid)
having a clear mind
Examples:
A lucid moment in his madness.