A vow is a serious, formal promise, often made publicly or in a ceremony. When people make a vow, they're declaring their commitment to do something or live a certain way, no matter what challenges arise.

The most familiar example is marriage vows, where couples promise to love and support each other “for better or worse.” Religious vows might include promises to serve a community or live according to certain principles. A knight in medieval times took vows of loyalty and courage. Someone might vow to tell the truth, to protect someone, or to achieve a difficult goal.

What makes a vow different from an ordinary promise? A vow carries more weight. It's meant to last, sometimes for a lifetime. When you vow to do something, you're saying “I will keep this promise no matter what happens.” Breaking a vow is considered more serious than breaking a casual promise because vows usually involve deeply important commitments.

You might hear someone say “I vow to practice piano every day” or “She vowed never to give up,” using the word to emphasize determination. The related word avow means to declare or admit something openly and firmly, while disavow means to deny any connection with something or to reject it completely.