Testator
Vine's Expository Dictionary of NT Words [1]
"to arrange, dispose," is used only in the Middle Voice in the NT; in Hebrews 9:16,17 , the present participle with the article, lit., "the (one) making a testament (or covenant)," virtually a noun, "the testator" (the covenanting one); it is used of "making a covenant" in Hebrews 8:10; 10:16; Acts 3:25 . In "covenant-making," the sacrifice of a victim was customary ( Genesis 15:10; Jeremiah 34:18,19 ). He who "made a covenant" did so at the cost of a life. While the terminology in Hebrews 9:16,17 has the appearance of being appropriate to the circumstances of making a will, there is excellent reason for adhering to the meaning "covenant-making." The rendering "the death of the testator" would make Christ a Testator, which He was not. He did not die simply that the terms of a testamentary disposition might be fulfilled for the heirs. Here He who is "the Mediator of a new covenant" ( Hebrews 9:15 ) is Himself the Victim whose death was necessary. The idea of "making a will" destroys the argument of Hebrews 9:18 . In spite of various advocacies of the idea of a will, the weight of evidence is confirmatory of what Hatch, in Essays in Biblical Greek, p. 48, says: "There can be little doubt that the word (diatheke) must be invariably taken in this sense of 'covenant' in the NT, and especially in a book so impregnated with the language of the Sept. as the Epistle to the Hebrews" (see also Westcott, and W. F. Moulton). We may render somewhat literally thus: "For where a covenant (is), a death (is) necessary to be brought in of the one covenanting; for a covenant over dead ones (victims) is sure, since never has it force when the one covenanting lives' [Christ being especially in view]. The writer is speaking from a Jewish point of view, not from that of the Greeks. "To adduce the fact that in the case of wills the death of the testator is the condition of validity, is, of course, no proof at all that a death is necessary to make a covenant valid. ... To support his argument, proving the necessity of Christ's death, the writer adduces the general law that he who makes a covenant does so at the expense of life" (Marcus Dods). See Appoint , Make.
Morrish Bible Dictionary [2]
One who makes a will or testament, introduced in Hebrews 9:16,17 in a parenthesis, showing that as a will is of force only after a man is dead, so Christ must have died for the blessings of the new covenant to be available.
King James Dictionary [3]
TESTA'TOR, n. L. A man who makes and leaves a will or testament at death.
Webster's Dictionary [4]
(n.) A man who makes and leaves a will, or testament, at death.