The adj lucid has 4 senses (first 1 from tagged texts)
1. (3) limpid, lucid, luculent, pellucid, crystal clear, perspicuous -- ((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. lucid -- (having a clear mind; "a lucid moment in his madness")
3. coherent, logical, lucid -- (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. crystalline, crystal clear, limpid, lucid, pellucid, transparent -- (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")