lucid in WordNet English dictionary

1. 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"
   coherent  logical  lucid 
   
2. (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"
   limpid  lucid  luculent  pellucid  crystal clear  perspicuous 
   
3. 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"
   crystalline  crystal clear  limpid  lucid  pellucid  transparent 
   
4. having a clear mind
   "a lucid moment in his madness"
   lucid