In the Book of Mormon, a number of people are described as "just men": Jacob (Enos 1:1), Benjamin (Omni 1:25), the kings and teachers of the Nephites from the time of Nephi to Benjamin (Mosiah 2:4), Helaman and Shiblon (Alma 63:2), Lachoneus (3 Nephi 3:12), Nephi3 (3 Nephi 8:1).
According to Donna Nielsen, the phrase "just man" was an expression for a strict observer of the Law (Geikie 111). [Donna B. Nielsen, Beloved Bridegroom: Finding Christ in Ancient Jewish Marriage and Family Customs, p. 24]
“My Father Was a Just Man”
Enos mentions that "my father . . . was a just man" (Enos 1:1). According to McConkie and Millet, a just man is one that has kept his covenants with exactness and honor. Just is a legal term derived from the Latin jus, meaning "right" or "law." An action that is justified in the eyes of the law is one which, upon examination, can be found to be right or lawful. Thus we read that Joseph the husband of Mary was "a just man" (Matthew 1:19), that Simeon, who blessed the Christ child in the temple, was "just and devout" (Luke 2:25), and that angels appear to "just and holy men" (Alma 13:26). [Joseph Fielding McConkie and Robert L. Millet, Doctrinal Commentary on the Book of Mormon, Vol. II, p. 96]
The definition of a "just man" is one who is righteous, lawful and upright in his dealings. One who speaks the truth and is fair. (Websters New World Dictionary, p. 795)