Lucid /panəˈsiːə/ adj.  

Definition:  Lucid is an adjective to describe something that is very clear and easily understood or comprehensible. It also refers to having a clear perception or understanding; able to think clearly and rationally, especially between periods of confusion or insanity. 

Lucid can also refer to something that is shining, bright, and radiant. 

Etymology: Derived from the Latin verb lucēre, meaning “to shine” via the Latin adjective lucidus, meaning “shining”. Originally, it meant “bright”, “shining” or “full of light”, but it is now more commonly used figuratively. It often describes the fleeting moments of clarity a person with dementia has sometimes when they are able to recognize their family and where they are in time and space.

In psychology and social settings, lucid commonly refers to a type of dream state. A lucid dream is one where the dreamer becomes aware of the fact that they are dreaming and continues to dream with this awareness. Sometimes the dreamer can change the circumstances of the dream or engage in activities that are impossible while awake, such as flying.

In a Sentence

She provided a lucid explanation of the events of the night.

He had a few fleeting, lucid moments over the course of his illness.

The lucid stars lit up the night sky.

Synonyms 

Luminous, Intelligible, Sane

Antonyms 

Ambiguous, Confusing, Muddled, Dim