What is the meaning of κύριος?

ruling, governing, having power

decisive, critical, authorized, valid, legal, entitled

fixed, set, appointed

literal

main, major, primary, principal

lord, master, guardian, ruler, owner

"Sir"

God (i.e., the God of Israel)

In the Septuagint, κύριος is regularly used to translate יהוה (a.k.a. the Tetragrammaton), as well as אֲדׂנָי.

During the Koine period, the nominative became more regular for direct address (as opposed to just the vocative).

Patristic usage expanded the use of κύριος to address the Holy Spirit as well.

mister (title conferred on an adult male)

master (someone who has control over something or someone)

sir (an address to any male)

main, principal, most important

Source: wiktionary.org