easily understood; completely intelligible or comprehensible

a lucid explanation.

characterized by clear perception or understanding; rational or sane

a lucid moment in his madness.

shining or bright.

clear; pellucid; transparent.

noun

clearness , distinctness , limpidity , limpidness , lucidity , pellucidity , pellucidness , perspicuity , perspicuousness , plainness , mind , reason , saneness , sense , soundness , wit