lucidity

Concise Oxford English Dictionary © 2008 Oxford University Press:
lucid /ˈluːsɪd/

▶adjective

• 1 clear; easy to understand.

  ■ showing an ability to think clearly.

  ■ Psychology (of a dream) in which the sleeper is aware of dreaming.

• 2 literary bright or luminous.

– derivatives
lucidity noun,
lucidly adverb.

– origin C16 (in sense 2): from L. lucidus (perh. via Fr. lucide or Ital. lucido) from lucere ‘shine’, from lux, luc- ‘light’.