a nation: a people group seen as a political and territorial body, with its own land, government, and identity
This is the word for a nation in the fullest public sense: a population that holds territory, has rulers, and stands as one body among the powers of the world. It pictures a people from the outside, by the marks a stranger would notice, its land, its kings, its armies, its sheer numbers, rather than from the inside by shared blood or family memory.
Because it views a people this way, it can name any nation at all, including Israel. God's promise to make Abraham into a great one of these (Genesis 12:2) and his calling of Israel to be a holy one (Exodus 19:6) use this very word, framing Israel as a real nation on the world stage. So do the lists in Genesis 10 that sort all of humanity into its peoples after the flood.
The heavy use of the plural for the surrounding peoples (see the second meaning) grew out of this basic sense and never fully separated from it. When the prophets scatter Israel "among the nations," the same word covers both Israel and the peoples she is scattered among.