Vine’s: “properly an adjective, signifying having power (kuros) or authority, is used as a noun, variously translated in the N.T., “’Lord,’ … ‘Master,’…”
Thayer’s: “he to whom a person or thing belongs, about which he has the power of deciding; master, lord… a. univ. of the possessor and disposer of a thing, the owner…b. kurios is a title of honor, expressive of respect and reverence, with which servants salute their teacher and master…”
The title “lord” was given to many in Bible times. It referred to rulers and heads of families. Sarah called Abraham “lord” (1 Pet. 3:5). However, as with many other common words, the Holy Spirit took this one and applied to in a special and unique way to Jesus the Christ.
Jesus is “Lord” in a way that no ruler or earthly father can claim. Peter declared Him to be “Lord and Christ” (Acts 2:36). He is Lord of lords, that is, Jesus rules over all others; there is no equal and certainly none superior (1 Tim. 6:15).
As the definitions above state, to be kurios is to possess power and authority, to be an owner, master—to have the right to decide, command. This designation and its meaning is aptly applied to Jesus. He possesses all authority in heaven and on earth (Matt. 28:18). He has the right to direct us in our lives.
Man will either acknowledge Jesus as Lord or reject Him. It is impossible to serve two masters (Matt. 6:24). We will either bow to the authority of Jesus or the devil. One is a legitimate Master the other a fraudulent miscreant. When we reach the age of accountability and commit sin, we put ourselves under the rulership of Satan. If we obey the gospel, we are redeemed from servitude to the cruel master to labor for our Lord and Savior (Rom. 6:16, 17). From that point on our loyalty belongs to One and only One. Our dedication and devotion, love and adoration—yes our whole mind, body, and soul belong to Him and are for His glory. He is our Lord and expects nothing less.