Concerning the meaning of the Latin word testamentum (genitive, testamenti), Edwin Hatch, in his work Essays in Biblical Greek, Oxford, 1889, p. 48, states that “in ignorance of the philology of later and vulgar Latin, it was formerly supposed that ‘testamentum,’ by which the word [di·a·the′ke] is rendered in the early Latin versions as well as in the Vulgate, meant ‘testament’ or ‘will,’ whereas in fact it meant also, if not exclusively, ‘covenant.’”
New World Translation. 1984 ed. p. 1585