LUCID broadly reduces to the three senses below. The Latin roots of ‘lucid’ signify: bright/shine/light.
1: mentally sane;
2: clear; easy to understand
3: giving forth light; shining; bright; luminous
(lucid dreaming is only given as a subsense in 1 dic.)
LUCIFER (the entry immedately following ‘lucid’ in all dics.) The correspondence is ‘light’ and/or ‘shining.’
Latin roots = light bringing/light bearing
1: morning star = the planet Venus when it rises in the morning
2: Satan; Prince of Darkness; Devil
3: match for striking a light
(Luciferous = emitting light)
UNLUCID = especially unintelligent, obscure
Lucidity relates to a clearness, soundness, even transparent, but these meanings are created by virtue of “light shining in.”
In ‘unlucid’, I presume there is a lack of light, perhaps this is “the darkness that obscures.”
LUCIFER is allegorical device meant to elucidate some estoteric or hermetic principle?