Concise Bible Dictionary:

In Gen. 43:2020And said, O sir, we came indeed down at the first time to buy food: (Genesis 43:20) the word is adon, often translated “Lord.” In the Acts (except in Acts 16:3030And brought them out, and said, Sirs, what must I do to be saved? (Acts 16:30)) the word is ἀνήρ, “man,” and is used as a term of respect. In all other places in the New Testament the word is κύριος, commonly translated “Lord”; in these cases the context determines how it should be rendered.