Both of the kings who were named Mosiah in the Book of Mormon are depicted as exemplary leaders of extraordinary practical and spiritual ability. Both were champions of justice and mercy. Considering that these individuals were anointed as kings, it may at first glance be tempting to assume that their names derive from the Hebrew word for Messiah, meaning "anointed." However, an even better possibility is that the name comes from the Hebrew word môšia? (mo-SHE-ah), meaning a "deliverer" or "savior."
Book of Mormon Central, "How Was Mosiah a Type of Christ? (Mosiah 26:12)," KnoWhy 104 (May 20, 2016).
John W. Welch, "What Was a ‘Mosiah’?" in Reexploring the Book of Mormon: A Decade of New Research, ed. John W. Welch (Provo, UT: FARMS, 1992), 105–107.