vow

Concise Oxford English Dictionary © 2008 Oxford University Press:
vow/vaʊ/

▶noun a solemn promise.

■ (vows) a set of such promises committing one to a prescribed role or course of action, especially marriage or a monastic career.

▶verb

• 1 solemnly promise to do something.

• 2 archaic dedicate to someone or something, especially a deity.

– origin ME: from OFr. vou, from L. votum (see vote); the verb is from OFr. vouer.