promisor

from WordNet (r) 3.0 (2006)

promisor
    n 1: a person who makes a promise [syn: {promiser}, {promisor}]

from The Collaborative International Dictionary of English v.0.48

Promisor \Prom"is*or\, n. (Law)
   One who engages or undertakes; a promiser. --Burrill.
   [1913 Webster]

from Bouvier's Law Dictionary, Revised 6th Ed (1856)

PROMISOR. One who makes a promise. 
     2. The promisor is bound to fulfill his promise, unless when it is 
contrary to law, as a promise to steal or to commit an assault and battery; 
when the fulfillment is prevented by the act of God, as where one has agreed 
to teach another drawing and he loses his sight, so that he cannot teach it; 
when the promisee prevents the promisor from doing what he agreed to do; 
when the promisor has been discharged from his promise by the promisee, when 
the promise, has been made without a sufficient consideration; and, perhaps, 
in some other cases, the duties of the promisor are at an end.