reign (n.) Look up reign at Dictionary.com
early 13c., "kingdom," from Old French reigne "kingdom, land, country" (Modern French règne), from Latin regnum "kingship, dominion, rule, realm," related to regere "to rule, to direct, keep straight, guide" (from PIE root *reg- "move in a straight line," with derivatives meaning "to direct in a straight line," thus "to lead, rule"). Meaning "period of rule" first recorded mid-14c.
reign (v.) Look up reign at Dictionary.com
"to hold or exercise sovereign power," late 13c., from Old French regner "rule, reign" (12c.), from Latin regnare "have royal power, be king, rule, reign," from regnum "kingship, dominion, rule, realm," related to regere "to rule, to direct, keep straight, guide" (from PIE root *reg- "move in a straight line," with derivatives meaning "to direct in a straight line," thus "to lead, rule"). Related: Reigned; reigning; regnal.