To make a solemn promise or pledge; to swear an oath. Commonly used at weddings or formal pledges.
結婚式で永遠の愛を誓った。
They vowed eternal love at the wedding.
彼は目標達成を誓ってトレーニングを始めた。
He pledged to achieve his goal and began training.
市長は任務を忠実に果たすことを誓った。
The mayor vowed to faithfully carry out his duties.