My lord. אֲדֹנִי. The singular form is constantly used in Hebrew, as in other languages, together with the plural personal pronoun (see at Genesis 23:6). The deference now paid to Moses (cf. Numbers 32:25, Numbers 32:27) is in marked contrast to the treatment he had received from the former generation.
Only Aaron (and that under the influence of terror—Exodus 32:22; Numbers 12:11) and Joshua (Joshua 11:1-23 :28) had addressed him as Adoni before.