i-adjective
Describes physical cleanliness or clarity, such as water, air, or a surface. Also used figuratively for a clear state of mind or conscience.
この川の水はとても清い。
The water in this river is very clean.
清い空気を吸う
Breathing clean air feels good.
i-adjective
pure; honest; innocent; chaste
Refers to moral purity, honesty, innocence, or chastity. Often used for a person's character, heart, or relationships. 'Platonic' is a specific nuance for non-romantic relationships.
彼は清い心の持ち主だ。
He is a person with a pure heart.
二人の関係は清い友情だ。
Their relationship is a pure friendship.