na-adjective
Describes visual beauty or attractiveness of people, objects, or scenes.
彼女はとても綺麗ですね。
She is very pretty, isn't she?
この花は本当に綺麗だ。
These flowers are really beautiful.
na-adjective
Describes cleanliness, order, or purity of objects, places, or abstract things. Often written in kana.
部屋をきれいに掃除した。
I cleaned the room thoroughly.
この水はとてもきれいだ。
This water is very clean.
na-adjective
Used adverbially as きれいに to mean doing something thoroughly or without leaving anything behind. Often written in kana.
宿題をきれいに忘れてしまった。
I completely forgot about my homework.
彼はきれいに姿を消した。
He disappeared entirely.