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to swear; to vow; to take an oath; to pledge
二人は永遠の愛をお互いに誓った。
The two vowed eternal love to each other.
神の前で結婚の誓いを正式に立てた。
They formally made their marriage vows before God.
彼は禁煙を固く誓ったが続かなかった。
He firmly vowed to quit smoking but couldn't keep it up.