Boyd’s Bible Dictionary:

Second son of Shem (Gen. 10:22). Also Hebrew form for Assyria (Ezek. 27:23).

Concise Bible Dictionary:

In Genesis 10:11 it would appear from the AV (KJV) that a son of Ham named Asshur built Nineveh; and then in Genesis 10:22 and 1 Chronicles 1:17 Asshur is named as the son of Shem. But in the margin of Genesis 10:11 it reads that “he went out into Assyria,” that is, Nimrod went forth into Asshur or Assyria (the Hebrew is the same). This is confirmed by Micah 5:6, where Assyria and Nimrod are associated together. Assyria is traced to Asshur or Assur, a son of Shem. Nimrod came afterward and may have subdued the country, but with what result is not shown.

Jackson’s Dictionary of Scripture Proper Names:

a step