Alma 8:7

Now it was the custom of the people of Nephi, to call their lands, and their cities, and their villages, yea, even all their small villages, after the name of him who first possessed them; and thus it was with the land of Ammonihah.

Nephi’s people had a custom. They named their lands, cities, and villages after the first person who lived there. That’s how the land of Ammonihah got its name.

The Nephites had a custom of naming their lands, cities, and villages after the first person who settled them. That’s how Ammonihah got its name.