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to sink; to go under; to submerge
to go down (e.g. sun); to set; to descend
to feel depressed; to become subdued; to become somber
太陽がゆっくりと沈んでいく。
The sun is slowly sinking.
太陽が西の空にゆっくり沈む。
The sun slowly sets in the western sky.
船が嵐で海に沈んでしまった。
The ship sank into the sea due to the storm.