make a vow—make a solemn promise or undertaking:
- There is a sect called the Abstinents who make a vow to abstain from everything that has enjoyed life, and to eat nothing but vegetables.
make one’s vows—(also: make the vows) join a religious order; become a monk or nun:
- He made his vows two years later and studied for the priesthood under the direction of the pious Abbot Pfluger.