In the book Among the Gentiles, Luke Johnson points out the term “Lord” was used of gods in the ancient world:

The title “Lord” (kyrios) was probably the earliest used by the first believers to express their conviction that Jesus was exalted to a share in God’s’ power (1 Cor 12:3; Rom 10:9).48 Writing to the Philippian church, Paul declares that “God has greatly exalted him and has given him a name above every name, so that at the name of Jesus every knee should bend, above the heavens and upon the earth and in the depths, and every tongue should confess that Jesus Christ is Lord” (Phil 2:9-11). In the Greco-Roman world, this designation for the divine was common: we have noted how Aelius Aristides spoke of “Lord Serapis” and “Lord Asclepius.” It was, in fact, the connection of this title to Hellenistic cults that led to the theory that the Jesus movement only became the “Christ cult” when it went outside Palestine and encountered Greco-Roman religion.