Easton's Bible Dictionary

Testament - occurs twelve times in the New Testament (Heb. 9:15, etc.) as the rendering of the Gr. diatheke, which is twenty times rendered "covenant" in the Authorized Version, and always so in the Revised Version. The Vulgate translates incorrectly by testamentum, whence the names "Old" and "New Testament," by which we now designate the two sections into which the Bible is divided. (See BIBLE)