The Collaborative International Dictionary of English v.0.48:

Testator \Tes*ta"tor\, n. [L.: cf. F. testateur.] (Law)
   A man who makes and leaves a will, or testament, at death.
   [1913 Webster]

WordNet (r) 3.0 (2006):

testator
    n 1: a person who makes a will [syn: testator, testate]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "testator":
   Maecenas, Santa Claus, almoner, almsgiver, angel, assignor,
   awarder, backer, bestower, cheerful giver, conferrer, consignor,
   contributor, donator, donor, fairy godmother, feoffor, financer,
   funder, giver, grantor, imparter, lady bountiful, patron,
   patroness, philanthropist, presenter, settler, subscriber,
   sugar daddy, supporter, testate, testatrix, vouchsafer



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

TESTATOR. One who has made a testament or will.
     2. In general, all persons may be testators. But to this rule there are
various exceptions. First, persons who are deprived of understanding cannot
make wills; idiots, lunatics and infants, are among this class. Secondly,
persons who have understanding, but being under the power of others, cannot
freely exercise their will; and this the law presumes to be the case with a
married woman, and, therefore, she cannot make a will without the express
consent of her husband to the particular will. When a woman makes a will
under some general agreement on the part of the husband that she shall make
a will, the instrument is not properly a will, but a writing in the nature
of a will or testament. Thirdly, persons who are deprived of their free will
cannot make a testament; as, a person in duress. 2 Bl. Com. 497; 2 Bouv.
Inst. n. 2102, et seq. See Devisor; Duress; Feme covert;, Idiot; Influence;
Parties to Contracts; Testament; Wife; Will.