na-adjective, noun
Describes something that is transparently clear, both literally (e.g., water, sky) and figuratively (e.g., thought, reasoning). Often used in literary or formal contexts.
彼の説明は明澄で、誰にでも理解できた。
His explanation was lucid and understandable to everyone.
明澄な湖の水が美しい。
The lucid water of the lake is beautiful.
Composed of 明 (bright, clear) and 澄 (clear, pure). The combination reinforces the idea of transparent clarity. The exact historical derivation is uncertain, but the kanji components directly suggest the meaning.