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to become clouded; to darken; to get dark; to become hidden (behind clouds)
to darken (of a face)
to worsen; to deteriorate; to become gloomy
ピクニック中に空が陰った。
The sky clouded over during the picnic.
空が次第に蔭ってきた。
The sky gradually became clouded.
悪い知らせに、母の顔が陰っていた。
Her mother's face had darkened at the bad news.