清
セイ, ショウ, シン, きよ.い, きよ.まる, きよ.める, あき, さや, し, すが, すみ, せ, ちん
pure, purify, cleanse, exorcise, Manchu dynasty
JLPT2 G4 S11 F705
As per 青# (clean/pure) + 水 water → *pure* water → *clear*; *clean*; *purify*. *Cool* is a borrowed meaning. The reading シン refers to the Manchu Dynasty (1644-1911). Note the variant form 淸.
[Full Kanji Etymology List]