reg·nant \-nənt\adjective Etymology: Latin regnant-, regnans, present participle of regnare to reign — more at reign 1.: exercising rule or authority : reigning < a queen regnant > 2. a.: having the chief power : exercising sway : dominant < filled with a regnant determination to defend herself — Gilbert Parker > b.: of common or widespread occurrence : prevalent < the vices regnant — Jonathan Swift >