The word Alma in Hebrew actually means young man, so, for some reason, Alma was named young man. You have here an interesting play on words. It says, "there was one among them whose name was Alma, he also being a descendant of Nephi. And he was a young man." (Mosiah 17:2).
A few years ago a Hebrew manuscript was discovered among the Bar Kochba scrolls down by the Dead Sea. They are not part of the Dead Sea scrolls, these were buried about 50 years after the Dead Sea Scrolls, during the Second Jewish revolt. It was a partnership sharing agreement between some owners of an orchard to divide up the harvest. One of the signators to this is a man named Alma Ben Yahudah, Alma, the son of Judah. This document was the first historical evidence found in which the name Alma was used for a man.
Matthew L. Bowen, "Alma — Young Man, Hidden Prophet," Interpreter: A Journal of Latter-day Saint Faith and Scholarship 19 (2016): 343–353.
Paul Y. Hoskisson, "What’s in a Name? Alma as a Hebrew Name," Journal of Book of Mormon Studies 7, no. 1 (1998): 72–73.