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 (see regal). 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 (see reign (n.)). Related: Reigned; reigning; regnal.