In this setting, the king over the greater land of Nephi wanted to have a name by which all of the converts could be called. He and Aaron settled on the name “Anti-Nephi-Lehies” (23:16). This name embraces the land of Nephi, the common ancestry back to Lehi, and the idea that these converts are now a part of the Nephites.
There are a good number of names that begin with the prefix anti. Antionum, Antipas, Antipus, antion, and then of course there is the Anti-Christ. The anti in anti-Christ means something completely different from the usage here. Anti-Christ, it means against Christ. Transliterated words such as Antionum, are Nephite words with Nephite syllables.
We do not really know what anti means. That is one of the things I want to look up in the Nephite dictionary when we finally get it. This name may simply have designated “descendants of Lehi who are not descendants of Nephi,” or as we might say “non-Nephite Lehites.” But a better possibility is that it comes from the Egyptian nty, which means “the one who,” or “of,” or “part of.” In other words, these people wanted to be known as descendants of Lehi who were part of the Nephite religious order.
Book of Mormon Central, “Why Did Converted Lamanites Call Themselves Anti-Nephi-Lehies? (Alma 23:17),” KnoWhy 131 (June 28, 2016).
“Anti-Nephi-Lehi,” Book of Mormon Onomasticon.