late 14c., "righteous in the eyes of God; upright, equitable, impartial; justifiable, reasonable," from Old French juste "just, righteous; sincere" (12c.), from Latin iustus "upright, equitable," from ius "right," especially "legal right, law," from Old Latin ious, perhaps literally "sacred formula," a word peculiar to Latin (not general Italic) that originated in the religious cults, from PIE root *yewes- "law" (cf. Avestan yaozda- "make ritually pure;" see jurist). The more mundane Latin law-word lex covered specific laws as opposed to the body of laws. The noun meaning "righteous person or persons" is from late 14c.