Kyrios — Lord
אֲדֹנָי / יהוה
Lord — the LXX's rendering of BOTH YHVH and Adonai; when the NT quotes 'the Lord' from the Tanakh, the Name usually stands behind it.
The most theologically loaded translation choice in history: one Greek word carrying the Tetragrammaton. When the earliest confession says 'Yeshua is Kyrios,' both traditions recognize exactly what mantle that word wears — which is why it divided, and still defines, the conversation between them.
First occurrence
Matt 1:20 — 'An angel of the Lord appeared'
Key passages
Matt 4:10 — 'You shall worship the Lord your God' (quoting Deut 6)
Acts 2:36 — 'God has made Him both Lord and Messiah'
Phil 2:11 — 'Every tongue confess that Yeshua the Messiah is Kyrios'
Rom 10:13 — 'Whoever calls on the name of the Lord' (quoting Joel — YHVH)
In the Greek Scriptures
Κύριος