RAW entry - kurios

This week's cluster appears over 660 times in the New Testament:

G2962	κύριος	kurios	noun	lord, master	from kuros
G2959	κυρία	kuria	noun	lady {Cyria}
G2960	κυριακός	kuriakos	adj	lord’s kind
G2961	κυριεύω	kurieuo	verb	be lord
G2634	κατακυριεύω	katakurieuo	verb	exercise lordship	from G2596 G2961
G2963	κυριότης	kuriotes	noun	lordship

The "lord" or "master" has complete authority over his subjects. The basic relationship is a master to a slave. The slave must do whatever the master says. The master also provides for the slave's needs.
Consider how frequently Jesus is named "Lord" in the NT.

When strangers addressed one another, they might us κύριος as a courtesy. We might address any man "Excuse me, sir..." even though he is not actually a knight. Likewise "lord" is meant to show some willingness to serve (listen to the Samaritan woman when Jesus asked her to draw water for him in John 4:11). 


Most English Bibles use "LORD" in the OT for the proper name of God, YHWH. At some point, Jews made it the practice not to speak God's name to prevent using it in vain--one of the Ten Commandments in Exodus 20:7--and replace it with adonai Lord.
The Hebrew scriptures still have YHWH written throughout, but adonai is spoken in its place. The LXX, translated around 150 BC, uses "lord" in place of every instance of YHWH. Since YHWH never appears in the NT, this practice must have pre-dated Jesus.