1) He swears 2) Oath giver 3) Oath taker 4) One who makes promises 5) One who promises 6) Party to a promise 7) Promise maker 8) Promiser 9) Promisor 
• (n.) One who makes a vow.
Vow'er noun One who makes a vow. Bale. 
[n] - someone who makes a solemn promise to do something or behave in a certain way
noun 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`