Lucid
WordNet
adjective
(1) (of language) transparently clear; easily understandable
"Writes in a limpid style"
"Lucid directions"
"A luculent oration"- Robert Burton
"Pellucid prose"
"A crystal clear explanation"
"A perspicuous argument"
(2) Transmitting light; able to be seen through with clarity
"The cold crystalline water of melted snow"
"Crystal clear skies"
"Could see the sand on the bottom of the limpid pool"
"Lucid air"
"A pellucid brook"
"Transparent crystal"
(3) Capable of thinking and expressing yourself in a clear and consistent manner
"A lucid thinker"
"She was more coherent than she had been just after the accident"
(4) Having a clear mind
"A lucid moment in his madness"