term:

Vow

vow n

: a solemn promise or statement
;esp
: one by which a person is bound to an act, service, or condition [marriage s]
vt 1 : to promise solemnly
2 : to bind or commit by a vow
vi
: to make a vow
vow·er n

Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.