The Collaborative International Dictionary of English v.0.48:

Vow \Vow\, v. i.
   To make a vow, or solemn promise.
   [1913 Webster]

         Better is it that thou shouldest not vow, than that
         thou shouldest vow and not pay.          --Eccl. v. 5.
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The Collaborative International Dictionary of English v.0.48:

Vow \Vow\, n. [OE. vou, OF. vou, veu, vo, vu, F. v?u, from L.
   votum, from vovere, to vow. Cf. Avow, Devout, Vote.]
   [1913 Webster]
   1. A solemn promise made to God, or to some deity; an act by
      which one consecrates or devotes himself, absolutely or
      conditionally, wholly or in part, for a longer or shorter
      time, to some act, service, or condition; a devotion of
      one's possessions; as, a baptismal vow; a vow of poverty.
      "Nothing . . . that may . . . stain my vow of Nazarite."
      --Milton.
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            I pray thee, let me go and pay my vow. --2 Sam. xv.
                                                  7.
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            I am combined by a sacred vow.        --Shak.
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   2. Specifically, a promise of fidelity; a pledge of love or
      affection; as, the marriage vow.
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            Knights of love, who never broke their vow;
            Firm to their plighted faith.         --Dryden.
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The Collaborative International Dictionary of English v.0.48:

Vow \Vow\, v. t. [imp. & p. p. Vowed; p. pr. & vb. n.
   Vowing.] [OE. vouen, OF. vouer, voer, F. vouer, LL. votare.
   See Vow, n.]
   [1913 Webster]
   1. To give, consecrate, or dedicate to God, or to some deity,
      by a solemn promise; to devote; to promise solemnly. "When
      thou vowest a vow unto God, defer not to pay it." --Eccl.
      v. 4.
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            [Men] that vow a long and weary pilgrimage. --Shak.
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   2. To assert solemnly; to asseverate.
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WordNet (r) 3.0 (2006):

vow
    n 1: a solemn pledge (to oneself or to another or to a deity) to
         do something or to behave in a certain manner; "they took
         vows of poverty"
    v 1: make a vow; promise; "He vowed never to drink alcohol
         again"
    2: dedicate to a deity by a vow [syn: vow, consecrate]

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "vow":
   Bible oath, affirm, and candle, assert, assert under oath,
   asseverate, assurance, assure, attest, avouch, avouchment, avow,
   book, certify, confess, countersign, covenant, declare, depone,
   depose, express the belief, extrajudicial oath, faith, guarantee,
   ironclad oath, judicial oath, kiss the book, loyalty oath,
   make a promise, oath, oath of allegiance, oath of office,
   official oath, parole, pledge, plight, profess, promise,
   solemn declaration, solemn oath, state, swan, swear, swear by bell,
   swear the truth, swear to, swear to God, swear to goodness,
   test oath, testify, troth, underwrite, vouch, warrant, warranty,
   word, word of honor