No longer Greek to me?

It's amazing the things one finds on the Web these days while looking for something else. I was looking for how the term "New Testament" is traditionally rendered in Greek, and I found a really great website, http://www.ellopos.net/elpenor/greek-language.asp to learn to read the Greek language that I didn't want to lose. They also had an embeddable menu to all of the Septuagint & New Testament books in Greek:

I also found a wealth of Greek texts at http://www.tlg.uci.edu/demoinfo/demoauthors.php

I found all this because I was trying to find out why the books were styled 'Testament' in English. The latin Novo Vulgata uses 'Vetus Testamentum & Novum Testamentum'; I'd always assumed that the term was used because it was a testament as in that given in court by witnesses. 'Testimony' is rendered by the Greek words μαρτυρία or βεβαίωση or κατάθεση δικαστικ, which are all terms that have nothing to do with it. I finally found that the Greek Καινή Διαθήκη = New Testament and Παλαιά Διαθήκη = old Testament in the Greek used in most Christian Bibles.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In the Septuagint διαθηκη is regularly used as the translation of the covenant of God (berith), rather than the apparently more available word συνθηκη. In this there is already an expression of the fact that the covenant of God does not have the character of a contract between two parties, but rather that of a one-sided grant. This corresponds with the covenant-idea in the Old Testament, in which berith, even in human relations, sometimes refers to a one-party guarantee which a more favored person gives a less favored one (cf. Josh. 9:6, 15; 1 Sam. 11:1; Ezek. 17:13). And it is most peculiarly true of the divine covenantal deed that it is a one-party guarantee. It comes not from man at all, but from God alone. ~ Herman Ridderbos, The Epistle of Paul to the Churches of Galatia (Grand Rapids: Eerdmans, 1953), pp. 130-31.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In the Septuagint, διαθηκη (diatheke) was used for the Hebrew word ברית (berith) which can mean a a legal pledge or disposition or a one-sided promise. Berith is rendered diatheke in every passage where it occurs with two exceptions: Deut. 9:15 (marturion) and I Kings 11:11 (entole). The Greek word διαθηκη (diatheke), usually translated "covenant" in English Bibles, denotes a formal and legally binding declaration of benefits to be given by one party to another, with or without conditions attached. In secular contexts it was most often used of a "last will and testament."

Here's a link to the wonderful10-volume theological dictionary entry on διαθηκη
Theological Dictionary of the New Testament, Volume 2
by Gerhard Kittel, Gerhard Friedrich