Supreme Lord

The Greek word for lord is indeed used in scripture in the sense of master, and as a mere honorary title as in the English “Sir.” But, on the other hand, it is the translation of Adonai, “supreme Lord,” an incommunicable name of God, and the substitute for Jehovah, a name the Jews would not pronounce. It is in this sense that Christ is ‘the Lord, the Lord of lords, the Lord God’; Lord in that sense in which God alone can be Lord—having a dominion of which divine perfection is the only adequate or possible foundation. This is the reason why no one can call him Lord, but by the Holy Ghost. It is a confession which implies the apprehension of the glory of God as it shines in Him. It is an acknowledgment that He is God manifested in the flesh. Blessed are all who make this acknowledgment with sincerity; for flesh and blood cannot reveal the truth therein confessed, but only the Father who is in heaven. - Charles Hodge

Source unknown