lucid

(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”

having a clear mind

• “a lucid moment in his madness”

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”

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 cristal”