Source : Webster's Revised Unabridged Dictionary (1913)

Vower \Vow"er\, n.
   One who makes a vow. --Bale.

Source : WordNet®

vower
     n : someone who makes a solemn promise to do something or behave
         in a certain way; "young vowers of eternal love"; "there
         are many vowers of chastity but few who observe it"