Mosiah 16:8 says, "But there is a resurrection, and therefore the grave hath no victory and the sting of death is swallowed up in Christ." Isaiah 25:8 had said, "He will swallow up death in victory," and now Abinadi glosses that by saying "swallowed up in Christ." Similar language also occurs later in Alma 22:14, when Ammon is speaking to King Lamoni: "the grave shall have no victory, and that the sting of death should be swallowed up in the hopes of glory" (Alma 22:14). Death, then, is being swallowed up in victory, in Christ, and in hope.
Interestingly, the word in Hebrew in the Isaiah passage that underlies all these passages is netsach (ntsch). The word netsach can indeed mean victory. It can also mean the victor, the one who is preeminent, or the leader who brings about the victory. It can also mean the hope for victory, not referring just to a past victory, but also to the sense of optimism that there will be a victory. So, all three of these meanings, victory, Christ (the victor), and hope are contained in that word. Abinadi may well have known the passage in Isaiah 25 that he was using, and understood it as a reference to being swallowed up in Christ, just as Abinadi had modified the line in Isaiah 52 to read, "the Son reigneth." In quoting Isaiah 25:8, Abinadi may have realized that the priests would not have drawn that similar meaning out of the word netsach alone, and so he glossed it to render it as "death is swallowed up in Christ." That would be a perfectly legitimate translation or comment on that word. The plan of the priests was obviously to try to catch Abinadi in some inconsistency with the words of Isaiah the prophet, but they could not. Abinadi knows what he is talking about. I hope this information helps you to appreciate Abinadi’s masterful rebuttal and interchange with the priests of Noah.
David. Larsen, "Death Being Swallowed Up in Netzach in the Bible and the Book of Mormon," BYU Studies Quarterly 55, no. 4 (2016): 123–134.
Neal Rappleye, "’Swallowing Up’ Death in Isaiah, 1 Corinthians, and the Book of Mormon," Book of Mormon Central Blog (September 3, 2019).