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to be perfectly clear (water, air, etc.); to clear up
澄み切った山の湖は、周囲の峰々を鏡のように映していた。
The perfectly clear mountain lake reflected the surrounding peaks like a mirror.
台風後、空気が澄み切って遠くまで見通せた。
After the typhoon, the air was perfectly clear, and one could see far into the distance.
冬の朝は空が澄み切る。
On winter mornings, the sky tends to be perfectly clear.